Where does non-locality originate in dBB theory?

[Demystifier]

I'd add, dBB is pretty mysterious by my standards too, and I agree that it isn't realistic (EPR), but that's the point, right? It can match QM because it doesn't incorporate realism AND non-locality... you get locality via a pilot wave, but not realism.

It's actually the exact opposite. You get NON-locality via the pilot wave, but you get realism.

Concerning ćevapčići, I agree with everything said above.

 

[DevilsAvocado]

edit: gaze upon the glory of the coming of the pork!

Great nismaratwork! Do you think you can find a just slightly bigger picture...? I have lost my glasses and all I see is a blurry non-realistic picture of that you do a couple of hours after you have eaten...

(Use the attach/preview function for god’s sake! )

By the way I’m from Sweden, and I had a Polar Bear (Ursus maritimus) and two bottles of Absolut Vodka for breakfast, and it tasted... well pretty much as yesterday...

 

[DevilsAvocado]

If I understand you correctly, you reason in the following way. With superdeterminism, we can avoid nonlocality. So why do we deal with a nonlocal superdeterministic theory, such as Bohmian mechanics?

Correct.

The answer is simple: Because it is MUCH EASIER to construct a nonlocal (Bohmian) superdeterministic theory that agrees with predictions of QM, than a local one. There are people who struggle with construction of an explicit local superdeterministic theory (like 't Hooft), but it is much more difficult to do it, even if possible in principle.

Ahh! This explains it, and proves that I need to learn more about dBB.

I take it that this (of course) is in respect of mathematical formulations (what else!? ). I don’t know if this interest you, but the reason a layman like me can come to this conclusion, is that from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of: You have to know the state of all particles in the universe? And Even those outside the observable universe? And if the universe is infinite, that would mean infinite data? And if you want to do "some calculations", what particle do you start with? They all effect each other nonlocally and instantaneous? And how do you define a universal NOW? You would need to build a computer with infinite computer power, which is impossible? And is Superdeterminism really compatible with Gödel's incompleteness theorems?

Etc, etc, etc...

I have experience from computers and databases, and practical experience of the utterly mess that can happen when a lot of users want to access/modify the same data at the same moment... Maybe that’s why I’m "skeptic" to a universe that works in the somewhat same instantaneous "messy manners"... The solution to avoid this is timestamps + rigid rules + transaction management, and first in, first out.

"The only reason for time is so that everything doesn't happen at once." -- Albert Einstein​

Alice, of course, is capable of reading the measurement of her polarizer, but here the point is that she (as well as Bob) cannot CONTROL the reading of her/his measurement apparatus, in the sense that they cannot make the apparatus to be in the state they WANT. For that reason, they do not interpret nonlocal correlations as true exchange of information.

I agree that Alice cannot control the reading of her measurement apparatus = outcome is always 100% random. BUT if the polarizers are aligned parallel and Alice "first" measure 1 (or up), THEN she forces Bob to measure 0 (or down) unconditionally (if it’s that the kind of BBO we use, can also be 1/1), right?

See, however, a way to (apparently) avoid this problem as well, leading to a possibility to use entanglement for an (apparent) superluminal communication:
http://xxx.lanl.gov/abs/1006.0338

Okay, I’ll check out the paper and get back. Thanks for your answers, I really appreciate it!

 

[ThomasT]

Have you ever had merguez sausage? It's very much like that, but usually made of pork and less spicy... it's amazingly good.

In an omelet it's basically a porkgasm.

I'd add, dBB is pretty mysterious by my standards too, and I agree that it isn't realistic (EPR), but that's the point, right? It can match QM because it doesn't incorporate realism AND non-locality... you get locality via a pilot wave, but not realism.

Thanks, that was more than I expected, or wanted. But gastronomically exciting.

Regarding dBB, yes it matches qm to a certain extent, but there are problems. I really like the conceptualization of particle AND wave. But then there's the mysterious 'quantum potential'. See, the problem is that any so-called alternative interpretation of standard qm always has to, in some way, incorporate the standard qm generation of probabilities and the standard qm interpretation of those probabilities in order to actually predict real world experimental results. So all we've got is standard qm with a bit of unnecessary fluff. That's it. That's what all alternative qm 'interpretations' amount to.

 

[Demystifier]

I take it that this (of course) is in respect of mathematical formulations (what else!? ). I don’t know if this interest you, but the reason a layman like me can come to this conclusion, is that from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of: You have to know the state of all particles in the universe? And Even those outside the observable universe? And if the universe is infinite, that would mean infinite data? And if you want to do "some calculations", what particle do you start with? They all effect each other nonlocally and instantaneous? And how do you define a universal NOW? You would need to build a computer with infinite computer power, which is impossible? And is Superdeterminism really compatible with Gödel's incompleteness theorems?

Yes, that interests me very much, because it helps me to understand why many people don't like dBB.

I especially like your point:
"from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of"
Now I perfectly understand what makes you think so. Yet, when dBB is viewed from a mathematical point of view, it looks remarkably simple. In fact, all except one equations in
http://xxx.lanl.gov/abs/1002.3226
are equations of "standard" purely probabilistic QM. Relativistic dBB adds ONLY ONE equation, which is the last equation, Eq. (23).

By the way, irrespective of dBB, I insure you that superdeterminism is compatible with Gödel's incompleteness theorems. But of course, to understand that, you need to understand the mathematical side of the Gödel's incompleteness theorems as well.

 

[inflector]

dBB is a mysterious theory. Not realistic in any sense.

Perhaps not realistic in the English language sense of the word outside of physics. But in the very specific quantum physics definition it is definitely realistic. The particles actually exist independent of the observation and the wavefunction is also a "real" entity that exists independent of the wavefunction.

The nonlocal aspect of the theory may seem odd but many of us don't find it any odder than the underlying reality of experimental observation.

I personally don't believe that we are restricted to instantaneous nonlocality by experiment. So while the formal definition of dBB as it stands is that the wavefunction depends on the instantaneous position of each and every particle in the universe, I believe there is room for a less encompassing wavefunction in a version of dBB that is to universally nonlocal. Our experiments, for example, don't rule out superluminal communication at say 10⁷ lightspeed. So, if there were some superluminal mechanism that could create causal relationships between entangled particles at 10⁷ lightspeed then this increased speed of causal connectivity would allow a much larger causal cone (like a light cone but superluminal).

So to me, the important aspects of dBB are:

1) It is realisitic - particles exist even when they are not being observed.

2) It is deterministic - i.e. particles have actual positions all the time even before measurement and those particles move in ways that are determined by the locations and momentum of all the other particles.

3) It is nonlocal - it is possible to have a superluminal causal connection.

I believe that a theory which is nonlocal but where the position of a particle or group of particles is not, in all cases, determined by every single one of the other particles in the universe still fits the spirit of a dBB interpretation. Ultimately, I expect that physics will find a theory of this sort behind the behavior of QM which we all find so puzzling.

And if you want to do "some calculations", what particle do you start with? They all effect each other nonlocally and instantaneous? And how do you define a universal NOW? You would need to build a computer with infinite computer power, which is impossible? And is Superdeterminism really compatible with Gödel's incompleteness theorems?

Ah, who said the Big Flying Spaghetti Monster created the universe with laws that would be computable by mere humans?

I personally believe that a rather simple explanation that leads to tremendous computation complexity is very likely to be underlying our rather complex current set of rules, i.e. QM with the Standard Model + General Relativity with the Standard Model of Cosmology. It is clear however, that simpler models that develop complexity through emergent phenomena are many orders of magnitude more computationally intensive. After all, it took around a year of supercomputer time to compute the mass of the proton and neutron ab initio using Lattice QCD, I suspect the individual protons and neutrons get their mass through rather simpler means.

 

[Demystifier]

I really like the conceptualization of particle AND wave. But then there's the mysterious 'quantum potential'.

If you accept that there is a particle AND a wave, and if you accept that wave determines the particle velocity, then THERE IS NO quantum potential. Or at least not as a fundamental new entity. The quantum potential is just a more complicated way to write otherwise simple equations of particle velocities determined by waves, with the only motivation to make dBB look more similar to classical mechanics. As long as simplicity is considered more important than similarity with classical mechanics, there is no need to introduce or mention the quantum potential at all.

 

[nismaratwork]

Great nismaratwork! Do you think you can find a just slightly bigger picture...? I have lost my glasses and all I see is a blurry non-realistic picture of that you do a couple of hours after you have eaten...

(Use the attach/preview function for god’s sake! )

By the way I’m from Sweden, and I had a Polar Bear (Ursus maritimus) and two bottles of Absolut Vodka for breakfast, and it tasted... well pretty much as yesterday...

heh... ok I get it, big picture

Demystifier: I stand corrected... dBB really isn't something I know more than the basics of, or thought I did. I appreciate the correction... you're well named.

 

[nismaratwork]

If you accept that there is a particle AND a wave, and if you accept that wave determines the particle velocity, then THERE IS NO quantum potential. Or at least not as a fundamental new entity. The quantum potential is just a more complicated way to write otherwise simple equations of particle velocities determined by waves, with the only motivation to make dBB look more similar to classical mechanics. As long as simplicity is considered more important than similarity with classical mechanics, there is no need to introduce or mention the quantum potential at all.

When you say particle and a wave, do you mean QM duality, or dBB Pilot Wave (real) and Particle (real)?

 

[Demystifier]

When you say particle and a wave, do you mean QM duality, or dBB Pilot Wave (real) and Particle (real)?

I mean the latter.

 

[nismaratwork]

I mean the latter.

OK, understood... that's what I believed dBB proposed in the first place, and much of what makes it a distinct theory that hasn't been culled along with everything except QM.

 

[DevilsAvocado]

heh... ok I get it, big picture

No worries mate. It’s just that my new 142" LED display isn’t delivered until Monday and my arm just give up scrolling infinitely horizontal... ()

@All you guys:
Even though I had Polar Bear for breakfast, it’s time for a refill. I think its Polarizer Bear on the menu. (Buuuhhhh :/)

Be back later... lot to answer.

 

[nismaratwork]

No worries mate. It’s just that my new 142" LED display isn’t delivered until Monday and my arm just give up scrolling infinitely horizontal... ()

@All you guys:
Even though I had Polar Bear for breakfast, it’s time for a refill. I think its Polarizer Bear on the menu. (Buuuhhhh :/)

Be back later... lot to answer.

Salt... in... wounds... *gasp* So cruel!

Now man up and buy this! http://www.gizmag.com/toob-dome-screen/12635/

 

[DevilsAvocado]

Now man up and buy this! http://www.gizmag.com/toob-dome-screen/12635/

Cool!

I’m canceling my order!

When thinking more about it... a Swedish guy has come up with an even simpler solution, the retail will be approx 200 bucks:

https://www.youtube.com/watch?v=<object width="640" height="385">
<param name="movie" value="http://www.youtube.com/v/rNsFSVhZi9w&fs=1&amp;hl=en_US&amp;rel=0&amp;color1=0x3a3a3a&amp;color2=0x999999"></param>
<param name="allowFullScreen" value="true"></param>
<param name="allowscriptaccess" value="always"></param>
<embed src="http://www.youtube.com/v/rNsFSVhZi9w&fs=1&amp;hl=en_US&amp;rel=0&amp;color1=0x3a3a3a&amp;color2=0x999999" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed>
</object>

 

[DevilsAvocado]

Yes, that interests me very much, because it helps me to understand why many people don't like dBB.

I especially like your point:
"from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of"

Cool if I can help you in any way. (As I said, PF never stops to surprise me! )

Now I perfectly understand what makes you think so. Yet, when dBB is viewed from a mathematical point of view, it looks remarkably simple. In fact, all except one equations in
http://xxx.lanl.gov/abs/1002.3226
are equations of "standard" purely probabilistic QM. Relativistic dBB adds ONLY ONE equation, which is the last equation, Eq. (23).

That’s very interesting. I must tell you that to a layman there is some "lingual confusion" regarding dBB. It is called the de Broglie–Bohm theory, the Pilot-wave theory, Bohmian mechanics, and the Causal interpretation. So what is it, theory or interpretation...?
(When it comes to MWI, it’s 'just' an interpretation = no physical evidence [yet ].)

I wish I could understand the full extent of Eq. (23), I’m just guessing, but it looks like
(X1(s), . . . ,Xn(s))
is about "a statistical ensemble of particles", right?

Q1: Is your solution to making nonlocal reality compatible with relativity, unconditionally depending on a statistical ensemble of particles?
(Explanation to why this has caught my interest in next post.)

Q2: As I understand, the Born rule is the 'mechanism' behind probabilities in QM measurements <$$\psi|P_i|\psi$$>. Is there any explanation in dBB to the Born rule, to make it deterministic?

Because it is MUCH EASIER to construct a nonlocal (Bohmian) superdeterministic theory that agrees with predictions of QM, than a local one. There are people who struggle with construction of an explicit local superdeterministic theory (like 't Hooft), but it is much more difficult to do it, even if possible in principle.

(I have to take one step back and reconsider this)

Do we really have to bother with nonlocal/local if we explain the world in superdeterministic terms? What’s the problem? We run "ordinary" QM and conclude that the only reason we see entangled correlations between Alice & Bob is because everything we did in the EPR-Bell experiment was already settled from the Big Bang = no spooky action at a distance, just "plain & simple" superdeterminism?

Afaict, we can run the good old 1927 Copenhagen interpretation without any modification, and wind up with an "add-on" for the superdeterministic part (that 'acts' in a probabilistic way), sometime in the future (like http://arxiv.org/abs/0903.3680" ) ...

What am I missing?

 

[DevilsAvocado]

Do you actually ask "What is the Lorentz frame with respect to which the Bohmian force is instantaneous?". If THAT is your question, then the answer in the relativistic-covariant version of dBB is simple: If you repeat the experiment many times, then each time it will probably be ANOTHER Lorentz frame, because it (the Lorentz frame) is determined by initial conditions on Bohmian spacetime positions, which are usually different in each repeat of the experiment.

According to Special Relativity, depending on which frame of reference you are, you will see Alice first performing her measurement and thereby decohere the shared wavefunction, and decide what Bob will measure. In another frame of reference you will see the opposite, Bob will decide what Alice will measure. And in a third frame of reference, all will be simultaneous.

See #33, and a quote from the paper:
R: "... However, due to the superluminal influences, 'prior' does not always need to mean 'at an earlier time'."

The following quotes may also help:

On nonrelativistic BM:
No one can understand this theory until he is willing to think of psi as a real objective field rather than just a 'probability amplitude'.
John S. Bell

On relativistic BM:
No one can understand this theory until he is willing to think of x as a position in a 4-dimensional space, rather than just a collection of two conceptually different entities: 3-space position and 'time'.
H.N.

Let’s take it conceptually step by step. This is the setup:

• A laser source produces entangled pairs of photons through a BBO crystal.
  
  
• There measuring polarizers are separated by 20 km, and it takes light 66 microseconds (10^-6) to travel 20 km (in vacuum) from Alice to Bob.
  
  
• The total time for electronic and optical processes in the path of each photon at the detector is calculated to be approximately 100 nanoseconds (10^-9).
  
  
• The settings of the polarizers at Alice & Bob are independently and randomly chosen every 100 nanosecond (10^-9).
  
  
• Type II PDC crystal is used, yielding anti-correlated photon pairs.
  
  
• When the polarizers are aligned parallel (0º/0º), the result will be [0, 1] or [1, 0] unconditionally, so-called perfect correlations.
  
  
• When the polarizers are aligned anti-parallel (0º/180º), the result will be [0, 0] or [1, 1] unconditionally, so-called perfect correlations.

EPR-Bell experiment according to traditional QM + Superdeterminism (yet to be discovered):

• Alice, Bob & Chris diced to run an EPR-Bell experiment to verify Bell's theorem. They think that it’s their own decision, when in fact all has been settled from the Big Bang.
  
  
• They "diced" to let the two polarizers vary randomly and independent between the two fixed values 0º & 180º. (They don’t know that there is nothing random in the universe.)
  
  
• They have setup two big laser beams to signal high in the air when an entangled photon hits the measuring apparatus. (This is a 'futuristic function', only possible when we get a 100% 'clean' entangled source.)
  
  
• Alice & Bob travel to their polarizer & measuring apparatus.
  
  
• Chris starts the laser source, and immediately he sees the two laser beams in the sky, simultaneously.
  
  
• Alice will see her laser beam light up the sky before Bob’s laser beam light up.
  
  
• Bob will see his laser beam light up the sky before Alice’s laser beam light up.
  
  
• They all get together to verify the results, and they see that there is a perfect correlation between Alice & Bob. There is no disagreement about that.
  
  
• But then they start analyze in what order things happened, and a big quarrel starts. They can’t agree on the order, and they know that the shared wavefunction for the entangled pair can only decohere/collapse ONCE! And they know that if Alice was first she would have settled the outcome unconditionally for Bob, and if Bob was first he would have settled the outcome unconditionally for Alice!? Total confusion arises...
  
  
• They can’t find a solution to the problem, and starts writing https://www.physicsforums.com/showthread.php?t=395509".
  
  
• What they don’t know is that there is no nonlocal-relativity-correlation-problem at all, because absolutely everything was settled from the beginning! Every atom and photon in the experiment was predestinated, including the "random" polarizers. There was no superluminal collapse of the shared wavefunction. All they saw was an ordinary relativity experiment, where observers do have different experience of the ordering of events, i.e. perfectly normal.

EPR-Bell experiment according to the de Broglie–Bohm theory:
(Due to my lack of understanding, this is obviously wrong and needs to be CORRECTED.)

• Everything is the same as in the first example, until Alice, Bob & Chris gets together to analyze the experiment.
  
  
• They come to the conclusion that even though the polarizers are randomly set at very high speed, in the last nanosecond when the polarizer is fixed, a superluminal pilot-wave is sent out to ensure that the two entangled photons shows a perfect correlation when measured. All this happens in the very last nanosecond, when the two entangled photons are "in flight".
  
  
• First they get a little confused... why a pilot-wave if everything including the outcome is already settled by superdeterminism? But they decide to leave this problem for now, because there are worse things...
  
  
• They realize that "the last nanosecond" is dependent on relativity. Alice before Bob, or vice versa? They know that there is no "voting facility" in the pilot-wave, one has to decide, but whom!?
  
  
• They all go crazy and decide to start terrorizing Demystifier on Physics Forum.

P.S. Both experiments were repeated with only ONE photon pair measured and then a pause for 1 hour, for 10 hours/day, during 100 days, to avoid any "ensemble interpretations" – with exactly the same outcome and problems.

 

[nismaratwork]

Let’s take it conceptually step by step. This is the setup:

• A laser source produces entangled pairs of photons through a BBO crystal.
  
  
• There measuring polarizers are separated by 20 km, and it takes light 66 microseconds (10-6) to travel 20 km (in vacuum) from Alice to Bob.
  
  
• The total time for electronic and optical processes in the path of each photon at the detector is calculated to be approximately 100 nanoseconds (10-9).
  
  
• The settings of the polarizers at Alice & Bob are independently and randomly chosen every 100 nanosecond (10-9).
  
  
• Type II PDC crystal is used, yielding anti-correlated photon pairs.
  
  
• When the polarizers are aligned parallel (0º/0º), the result will be [0, 1] or [1, 0] unconditionally, so-called perfect correlations.
  
  
• When the polarizers are aligned anti-parallel (0º/180º), the result will be [0, 0] or [1, 1] unconditionally, so-called perfect correlations.

EPR-Bell experiment according to traditional QM + Superdeterminism (yet to be discovered):

• Alice, Bob & Chris diced to run an EPR-Bell experiment to verify Bell's theorem. They think that is their own decision, when in fact all has been settled from the Big Bang.
  
  
• They "diced" to let the two polarizers vary randomly and independent between the two fixed values 0º & 180º. (They don’t know that there is nothing random in the universe.)
  
  
• They have setup two big laser beams to signal high in the air when an entangled photon hits the measuring apparatus. (This is a 'futuristic function', only possible when we get a 100% 'clean' entangled source.)
  
  
• Alice & Bob travel to their polarizer & measuring apparatus.
  
  
• Chris starts the laser source, and immediately he sees the two laser beams in the sky, simultaneously.
  
  
• Alice will see her laser beam light up the sky before Bob’s laser beam light up.
  
  
• Bob will see his laser beam light up the sky before Alice’s laser beam light up.
  
  
• They all get together to verify the results, and they see that there is a perfect correlation between Alice & Bob. There is no disagreement about that.
  
  
• But then they start analyze in what order things happened, and a big quarrel starts. They can’t agree on the ordering, and they know that the shared wavefunction for the entangled pair can only decohere/collapse once! And they know that if Alice was first she would have settled the outcome unconditionally for Bob, and if Bob was first he would have settled the outcome unconditionally for Alice!? Total confusion arises...
  
  
• They can’t find a solution to the problem, and starts writing https://www.physicsforums.com/showthread.php?t=395509".
  
  
• What they don’t know is that there is no nonlocal-relativity-correlation-problem at all, because absolutely everything was settled from the beginning! Every atom and photon in the experiment was predestinated, including the "random" polarizers. There was no superluminal collapse of the shared wavefunction. All they saw was an ordinary relativity experiment, where observers do have different experience of the ordering of events, i.e. perfectly normal.

EPR-Bell experiment according to the de Broglie–Bohm theory:
(Due to my lack of understanding, this is obviously wrong and needs to be CORRECTED.)

• Everything is the same as in the first example, until Alice, Bob & Chris gets together to analyze the experiment.
  
  
  [*]They come to the conclusion that even though the polarizers are randomly set at very high speed, in the last nanosecond when the polarizer is fixed, a superluminal pilot-wave is sent out to ensure that the two entangled photons shows a perfect correlation when measured. Al this happens in the very last nanosecond, when the two entangled photons are "in flight".
  
  
  [*]First they get a little confused... why a pilot-wave if everything including the outcome is already settled by superdeterminism? But they decide to leave this problem for now, because there are worse things...
  
  
  [*]They realize that "the last nanosecond" is dependent on relativity. Alice before Bob, or vice versa? They know that there is no "voting facility" in the pilot-wave, one has to decide, but whom!?
  
  
• They all go crazy and decide to start terrorizing Demystifier on Physics Forum.

P.S. Both experiments where repeated with only ONE photon pair measured and then a pause for 1 hour, for 10 hours/day, during 100 days, to avoid any "ensemble interpretations" – with exactly the same outcome and problems.

@Bolded portion... That's what really confuses me about dBB, and I also suspect it's a lack of knowledge on my part. To me, the concept of a Pilot Wave sounds like the hand of god, in the shape of the Schrödinger equation.

 

[DevilsAvocado]

@Bolded portion... That's what really confuses me about dBB, and I also suspect it's a lack of knowledge on my part. To me, the concept of a Pilot Wave sounds like the hand of god, in the shape of the Schrödinger equation.

Yeah agree, it will be very interesting to hear what DeM has to say...

 

[nismaratwork]

Yeah agree, it will be very interesting to hear what DeM has to say...

From what little I understand, Schrödinger 'trajectories' replace the standard QM sum over paths, and it's the pilot wave that causes interference... it still sounds odd to me. Then again, it's clear Demystifier is very familiar with this theory, and I know I'm not.

 

[DevilsAvocado]

From what little I understand, Schrödinger 'trajectories' replace the standard QM sum over paths, and it's the pilot wave that causes interference... it still sounds odd to me. Then again, it's clear Demystifier is very familiar with this theory, and I know I'm not.

Yeah that’s my understanding too. There’s only one problem – as soon as you start involving "superluminal stuff" – you will have trouble in SR. And this goes for all, including Schrödinger wavefunction, or Pilot wave, or Little Green Men working very fast...

It’s predestinated to be messy, just because there is ONE thing that settles the outcome for TWO, and Einstein won’t let go on this situation just that easy.

You can start speculate about foliation of space-time, or holographic, or any other complicated solution.

Or you can just say that Special Relativity is wrong.

Both options are extremely tough.

 

[inflector]

They realize that "the last nanosecond" is dependent on relativity. Alice before Bob, or vice versa? They know that there is no "voting facility" in the pilot-wave, one has to decide, but whom!?

@Bolded portion... That's what really confuses me about dBB, and I also suspect it's a lack of knowledge on my part. To me, the concept of a Pilot Wave sounds like the hand of god, in the shape of the Schrödinger equation.

I understand it this way (but please feel free to correct me Demystifier if I get this wrong): once you invoke the idea of superluminal communication, "the last nanosecond" is not dependent on relativity that is constrained to lightspeed. In normal relativity, due to the speed of light limit, you have different "time" for each particle as they are separated.

In some sense, in dBB the entanglement ties together the time of the two frames such that they can been looked upon as if they were not separated by distance, or are separated by an arbitrarily small distance. So from the perspective of the two entangled particles there is never a question of which measurement takes place first since they share clocks for the duration of their entanglement. We may not be able to tell as observers which happened first, but the particles can tell.

In my mind's picture, I see two entangled particles running off with an invisible connection in the 4th dimension so they are always touching and therefore share the same time with respect to that connection no matter how far away they are separated. Thus a measurement of one particle is simultaneously a measurement of the two entangled (connected in a hidden dimension) particles at once even though they are separated spatially in our 3D slice of the world.

NOTE: This is just my own internal analogy for understanding one way this might be possible (like the balloon analogy in cosmology), I'm not proposing any idea or theory that this is the way it actually works.

So for me, the idea that in dBB the wave function for a particle is dependent on all the other particles in the universe, is just a way of saying that these sorts of nonlocal connections can exist, not that they always exist all the time between every particle.

 

[nismaratwork]

I understand it this way (but please feel free to correct me Demystifier if I get this wrong), once you invoke the idea of superluminal communication, "the last nanosecond" is not dependent on relativity that is constrained to lightspeed. In normal relativity, due to the speed of light limit, you have different "time" for each particle as they are separated.

In some sense, in dBB the entanglement ties together the time of the two frames such that they can been looked upon as if they were not separated by distance, or are separated by an arbitrarily small distance. So from the perspective of the two entangled particles there is never a question of which measurement takes place first since they share clocks for the duration of their entanglement. We may not be able to tell as observers which happened first, but the particles can tell.

In my mind's picture, I see two entangled particles running off with an invisible connection in the 4th dimension so they are always touching and therefore share the same time with respect to that connection no matter how far away they are separated. Thus a measurement of one particle is simultaneously a measurement of the two entangled (connected in a hidden dimension) particles at once even though they are separated spatially in our 3D slice of the world.

NOTE: This is just my own internal analogy for understanding one way this might be possible (like the balloon analogy in cosmology), I'm not proposing any idea or theory that this is the way it actually works.

So for me, the idea that in dBB the wave function for a particle is dependent on all the other particles in the universe, is just a way of saying that these sorts of nonlocal connections can exist, not that they always exist all the time between every particle.

I understand what you're getting at, but then you introduce foliation and dBB starts to look like string theory without the TOE promise. Where's Demyst and Zenith when you need 'em.

 

[ThomasT]

In what sense is dBB "non-local"? Is there any way of interpreting non-locality in dBB as being due to local, but non-realist, effects?

In case this hasn't already been cited, it does seem thematic, and since you're online:

How can one find nonlocality in Bohmian mechanics?
http://arxiv.org/PS_cache/quant-ph/pdf/0311/0311108v1.pdf
Andrei Khrennikov

 

[ThomasT]

... I also suspect it's a lack of knowledge on my part.

On all our parts, I suspect, except for Demystifier, and maybe a few others at PF. From only a cursory knowledge of dBB, and little-researched preconcieved notions about it, I've made some statements about it, all of which I should probably retract (even if some of them might be approximately correct) and start from scratch. So, after a morning of learning a bit more about the rationale for, and the formal construction of, dBB, I definitely know two things. 1) I would like to actually learn it as best I can given certain time constraints, and 2) I'm not going to argue with Demystifier (or any other Bohmians) about any dBB-related considerations, including nonlocality, until I actually do become much more approximately fluent wrt it than I am now (which will probably be a while).

I only have a couple of minor conceptual difficulties with it which, if they persist, I can always ask DeMystifier about. I would ask him in this thread, however, 1) I like to work these things out on my own, and 2) this thread is specifically about dBB and nonlocality.

It's great that you and DA seem, at least for the present, interested in whatever Demystifier might teach us also. Of course, most of it's on the web (I'm assuming). But, I'm hoping that Demystifier can point us to what he thinks are the best sources for teaching non-experts about dBB (no offense, but I'm assuming that you're also a non-expert, and if not then I apologize). I don't think it will require learning any new 'languages'. Just, perhaps, a slight shift in one's thinking and the blocking out of any prejudices that one might have had wrt dBB. And I'm also hoping that you and DA , with your youth and intelligence, will motivate me, for however long you stay interested in it, to study this stuff in order to keep up. I'm anticipating an intensive study program of about two to three weeks to get a good handle on this stuff. (By "intensive" I mean 12 to 16 hour days of looking at the dBB formulation, considering its relationship to standard qm, its possible implications, its possibilities, etc., etc., while, in my case at least, consuming copious amounts of popcorn and beer, my favorites, with an occasional break for pizza, and ... sleep?)

Bottom line for me is, Bohm was a really smart dude. I learned (what I can readily recall of) qm from the Dover edition of his 1950 textbook on quantum theory. And what I know of his philosophical/metaphysical worldview is very much in line with the way I've come to think about things.

To me, the concept of a Pilot Wave sounds like the hand of god, in the shape of the Schrödinger equation.

I don't think it's like that at all. But hopefully Demystifier will elaborate/explain.

 

[LukeD]

Wow, I haven't checked back on this thread in a little while. I wasn't expecting so much activity.

No!
Poisson equation is local, but acceleration of ONE particle CANNOT be calculated by knowing ONLY the solution of the of the Poisson equation and position of that particle. Instead, you must also know the positions of all other particles.

I believe I disagree with you on interpretation here.
Just because you need to know the positions of all other particles to calculate the gravitational field does not make Newtonian gravity non-local in my eyes.

The dynamics still arise from the Poisson eq, which is a local law. However, the Poisson equation's field propagates infinity fast, so we need to know all of the positions of each particle to calculate the dynamics accurately.
So to me, this is "non-local" in the sense that it is local, but that the field propagates infinitely fast.
And IMO, this is great because when we go from Newtonian Gravity to GR, the propagation speed changes from infinity to c. Clearly then, the gravitational field is local by just about anyone's definition.

Similarly, in dBB, we have that the dynamics of the theory (at least if we talk about the theory involving a wave function in configuration space), are local but propagate infinitely fast. Of course it is also strange that the wave function is defined not in space, but in configuration space.

--
Edit: I should mention that below I'm talking about vanilla relativistic QM, and that I haven't studied this myself, so my understanding is via small discussions with my roommate. That is to say, I have no reason to believe I haven't said something wrong.
--

If we change to the Klein-Gordon equation, we still have a local law with infinitely fast propagation, but if we use the Dirac equation(s), we have particles & anti-particles that travel no faster than speed c. We get multiple local disturbances that propagate at finite speed and conspire together to create a law that looks non-local.

So the way it looks to me is: in Schroedinger-dBB, we have non-local dynamics that arise from a local law with infinitely fast propagation. When we move to the relativistic limit with the Dirac equation, this propagation becomes only finitely fast.

If what I have said is accurate (and I have my doubts), then I see no problem with calling dBB local (but with infinite propagation speed)

 

[ThomasT]

So to me, this is "non-local" in the sense that it is local, but that the field propagates infinitely fast.

This doesn't make any sense to me.

 

[LukeD]

Well Poisson's Equation in free space (Laplace's Equation)
$${\nabla}^2 \varphi = 0$$

Can be seen to be the limit of the Wave Equation
$${ \partial^2 u \over \partial t^2 } = c^2 \nabla^2 u$$
as the right side becomes much larger than the left (or as c^2 goes to infinity). So in free space, the Newtonian gravitational potential obeys a wave equation with infinite propagation speed.

Essentially, the Newtonian gravitation field looks just like the Electric Field if we take c->infinity and change some signs around so that the field is always attractive.

 

[DevilsAvocado]

I understand it this way (but please feel free to correct me Demystifier if I get this wrong): once you invoke the idea of superluminal communication, "the last nanosecond" is not dependent on relativity that is constrained to lightspeed. In normal relativity, due to the speed of light limit, you have different "time" for each particle as they are separated.

In some sense, in dBB the entanglement ties together the time of the two frames such that they can been looked upon as if they were not separated by distance, or are separated by an arbitrarily small distance. So from the perspective of the two entangled particles there is never a question of which measurement takes place first since they share clocks for the duration of their entanglement. We may not be able to tell as observers which happened first, but the particles can tell.

. . .

Thanks for the reply inflector. Except for the pros, we’re probably all more or less stumbling in the dark with this enigma.

I asked Demystifier about this:

What is Nikolic saying? Is Alice incapable of reading the measurement of her polarizer? I don’t understand?? Or does he mean that that entangled photons exchange superluminal signals, but this is somehow "delayed" to non-superluminal before Alice can actually read the measurement...??

And the answer was:

Alice, of course, is capable of reading the measurement of her polarizer, but here the point is that she (as well as Bob) cannot CONTROL the reading of her/his measurement apparatus, in the sense that they cannot make the apparatus to be in the state they WANT. For that reason, they do not interpret nonlocal correlations as true exchange of information.

See, however, a way to (apparently) avoid this problem as well, leading to a possibility to use entanglement for an (apparent) superluminal communication:
http://xxx.lanl.gov/abs/1006.0338

I totally understand that there is NO way to use entanglement for true communication. The individual outcome is 100% random. But in the case of "perfect correlation" there will be a causal superluminal relation between Alice & Bob – cause & effect. And there can only be ONE cause and ONE effect, and they are NOT "relativity interchangeable". We can disagree on which occurs first of any two events that are spatially separated. This is perfectly OK according to by Einstein's theory of relativity. But we CANNOT disagree on cause & effect, because that would create unsolvable http://en.wikipedia.org/wiki/Grandfather_paradox" .

I think we can (without any doubts) interpret the answer from Demystifier on my (stupid ) question about a "delay" as negative (of course!). Thus, there will be a "DIRECT CONNECTION" to the superluminal (instantaneous?) "dBB signal" and Alice & Bob’s polarizer and measuring apparatus.

I have absolutely no problem with "Closed timelike curves" or "Wormholes", in fact they are valid solutions to the equations of General Relativity.

[PLAIN]http://upload.wikimedia.org/wikipedia/commons/a/af/Worm3.jpg

Normally there is no trouble with a disagreement on the orderings of events, if they are NOT causally connected. Causality is what causes all the trouble...

Personally, I just can’t see how one can "lift out" the superluminal "dBB signal" from the reality of Special Relativity. The measuring apparatus will be in a "frame of reference" that obeys Special Relativity, and that "frame of reference" will decide when NOW is, and what "the last nanosecond" will mean. The superluminal "dBB signal" just has to "wait" for the "Special-Relativity-Polarizer" to stop, to be able to "decide" what the "instantaneous" outcome will be. I can’t see any other solution...

And my stationary version of Alice & Bob is very "nice" in respect of Special Relativity. I’m pretty sure we can setup a complete "stretchy-rubber-spacetime-mess" of moving apparatus and observers that can’t agree on anything when it comes to distances, elapsed times, and orderings of events.

This http://en.wikipedia.org/wiki/Lorentz_transformation" shows events in spacetime of an accelerating observer:

[URL]http://upload.wikimedia.org/wikipedia/commons/e/e4/Lorentz_transform_of_world_line.gif[/URL]

Check out this picture of http://upload.wikimedia.org/wikipedia/commons/9/96/Einstein_train_relativity_of_simultaneity.png" for an explanation:

http://upload.wikimedia.org/wikipedia/commons/9/96/Einstein_train_relativity_of_simultaneity.png"

To put it short: The superluminal dBB signal obeys the rotating polarizer, and the polarizer obeys Special Relativity, therefore the superluminal dBB signal must obey Special Relativity!

I think...

 

[nismaratwork]

Yeah, we definitely need Demystifier and Zenith8 to help us out here.

@ThomasT: I'm sure I must be wrong about the pilot wave, after all it's theory that matches the predictions of QM so "hand of god" can't be in it. I'd really like to learn more about spacetime foliation in dBB... that's the technical part that I find challenging, as opposed to conceptual challenges.

 

[LukeD]

In case this hasn't already been cited, it does seem thematic, and since you're online:

How can one find nonlocality in Bohmian mechanics?
http://arxiv.org/PS_cache/quant-ph/pdf/0311/0311108v1.pdf
Andrei Khrennikov

This paper doesn't at all treat entanglement (though it conjectures that entanglement propagates as a field) and only notes that there is no non-locality when we have no entanglement. However, his explanation of why this occurs is very similar to my thinking about dBB. I am a disappointed though that he doesn't back up his explanation with some math.

I wonder what our dBB experts think about the idea that non-locality is due to propagation of correlations through a field in configuration space.