Popper/Lande interpretation of QM

[Tam Hunt]

Karl Popper, the highly influential philosopher of science was unusual in that, as a philosopher, he had a large impact on science itself. He was actually listened to by physicists! He's best known, of course, for his falsifiability criterion for theories to be considered scientific, which has become de rigeur in most branches of science.

He's less well known for his commentary on quantum physics and his interpretation of the mathematical formalisms of quantum physics. In his 1982 Postscript to the Logic of Scientific Discovery - Vol. 2 being Quantum Mechanics and the Schism in Physics - Popper presented the most fully developed discussion of his "propensity field interpretation" of quantum mechanics, in "thirteen theses." He poses a hard-hitting critique of the Copenhagen school of QM, arguing for a realist, particle-based, non-deterministic interpretation in which the most basic pieces of nature are indeed particles, with real positions and momenta, even if we can't know them precisely, there is no wave/particle duality, there is no "collapse of the wave function" caused by a conscious observer, and most importantly an interpretation of the Schrodinger wave equation as applying only to epistemology - what we can know abouat nature, what nature actually is - and not supporting the notion that particles are in fact waves in some instances and particles in others (or as Schrodinger believed simply waves that seem particle-like in some situations).

His thirteen theses are based in large part on Alfred Lande's 1965 work, New Foundations of Quantum Mechanics. Lande was a strong proponent of the Copenhagen school until later in life becoming disillusioned with the Bohr/Heisenberg/Pauli dismissive approach to reality and causality.

Here is my paraphrase of his thirteen theses:

1. Quantum mechanics concerns statistical problems about matter and energy.
2. Statistical questions demand statistical answers.
3. Because quantum mechanics provides statistical answers to statistical problems, it is a mistake to insert an “observer” into quantum mechanics as a necessary component of “wave collapse.”
4. The “great quantum muddle” results from mistaking the wave function – the statistical answers of quantum mechanics – for a physical property of the particles at issue. The wave function is a mathematical device, not a physical property.
5. Heisenberg's uncertainty formulae are not actual limits on the precision of our knowledge, they are, rather, “statistical scatter relations.” “They thereby limit the precision of certain individual predictions.”
6. The statistical answers of quantum mechanics refer to populations of particles, which do, contrary to the Copenhagen Interpretation, have a real and precise position and momentum. (We cannot know with absolute precision, however, these data for any particular particle, but this does not mean the particle itself does not actually have a defined position and momentum).
7. Heisenberg effectively admitted the truth of the previous theses but the commonly accepted Copenhagen Interpretation has for some reason maintained the contrary views for the most part. Heisenberg was, however, on final reflection, agnostic about the reality of a given particle's past history, based on retrodictive measurements: “It is a matter of personal belief whether such a calculation concerning the past history of the electron can be ascribed any physical reality or not.”
8. The mistaken Copenhagen Interpretation is closely related to the common interpretation of the calculus of probability, which mistakes certainty (or lack thereof) about our knowledge of events in the world with the certainty (or lack thereof) of certain events actually happening. The objective “propensity interpretation” of probability calculus is the best approach for quantum physics, which avoids the mistake of the common interpretation. The “propensity field” indicates the likelihood of a certain outcome of the experimental arrangement. A given experimental arrangement's propensity field is a real physical quality, though a “somewhat abstract kind of physical quality.”
9. The collapse of the wave function is not an effect unique to quantum mechanics – it is an effect common to all probability theory. There is no more to the wave collapse in QM than the “trivial principle: if our information contains the result of an experiment, then the probability of this result, relative to this information (regarded as part of the experiment's specification), will always trivially be” 100 percent.
10. The propensity interpretation of probability calculus solves the problem of the relationship between particles and their statistics, that is, between particles and the wave function, because in Popper's interpretation there is a real particle, with defined position and momentum, and the propensity field of the entire experimental arrangement (or situations outside of any actual human experiment, though human knowledge will require an experiment).
11. It is misleading to speak of wave/particle duality or of a duality of particles and propensity fields. This is the case because propensity fields are properties of a given experimental arrangement, not of the particles that are the object of study. There is, therefore, no need for an “observer” to collapse the wave function because there is no “collapse” in a physical sense.
12. The mistaken idea of wave/particle duality arose from de Broglie and Schrödinger's attempts in the 1920s to create a wave theory of the structure of particles. These attempts failed, but the wave/particle duality interpretation was mistakenly retained.
13. Both quantum physics and classical physics are indeterministic. Popper doesn't clarify this point in his paper.


So my question is: who has actually heard of the Popper/Lande "propensity field" interpretation of QM and what do people think of these ideas as a more common-sense interpretation of the queer QM maths?

 

[DrChinese]

He's less well known for his commentary on quantum physics and his interpretation of the mathematical formalisms of quantum physics. In his 1982 Postscript to the Logic of Scientific Discovery - Vol. 2 being Quantum Mechanics and the Schism in Physics - Popper presented the most fully developed discussion of his "propensity field interpretation" of quantum mechanics, in "thirteen theses." He poses a hard-hitting critique of the Copenhagen school of QM, arguing for a realist, particle-based, non-deterministic interpretation in which the most basic pieces of nature are indeed particles, with real positions and momenta, even if we can't know them precisely, there is no wave/particle duality, there is no "collapse of the wave function" caused by a conscious observer, and most importantly an interpretation of the Schrodinger wave equation as applying only to epistemology - what we can know abouat nature, what nature actually is - and not supporting the notion that particles are in fact waves in some instances and particles in others (or as Schrodinger believed simply waves that seem particle-like in some situations).

...

The critique of CI falls flat given Bell's Theorem and the rise of entanglement experiments. So if his critique is to make sense, you must join the Bohmian school... a result which I doubt is intended. Probably why you don't really hear that much about Popper.

I usually hear his name associated with "theory falsification" concepts, an important philosophical idea. Hadn't heard of the "propensity field" as such.

 

[Demystifier]

The theses above correspond very well to what we call today (Ballentine) statistical ensemble interpretation. Concerning the last thesis that both quantum and classical mechanics are indeterministic, see also
http://xxx.lanl.gov/abs/quant-ph/0505143 [Found.Phys.Lett. 19 (2006) 553-566]
http://xxx.lanl.gov/abs/0707.2319 [AIPConf.Proc.962:162-167,2007]

 

[Tam Hunt]

Dr. Chinese, I am personally also more drawn to the Bohmian interpretation but I'm not sure that Bohm and Popper/Lande are entirely incompatible. Bohm's "implicate order" may be likened to Popper's "propensity fields," which he described as real but not physical - just as Bohm did the implicate order. Popper did in fact make much of entanglement, calling in the early 1980s after the Aspect experiments for a broad-scale revision of relativity and quantum theory - on the former claiming that the Aspect experiments undermined the idea of relative simultaneity, which is the basis for the entire edifice of relativity theory. Could you flesh out why you think Popper's theory can't deal with entanglement?

 

[Tam Hunt]

Thanks Demystifier, I'll check these out.

 

[DrChinese]

Dr. Chinese, I am personally also more drawn to the Bohmian interpretation but I'm not sure that Bohm and Popper/Lande are entirely incompatible. Bohm's "implicate order" may be likened to Popper's "propensity fields," which he described as real but not physical - just as Bohm did the implicate order. Popper did in fact make much of entanglement, calling in the early 1980s after the Aspect experiments for a broad-scale revision of relativity and quantum theory - on the former claiming that the Aspect experiments undermined the idea of relative simultaneity, which is the basis for the entire edifice of relativity theory. Could you flesh out why you think Popper's theory can't deal with entanglement?

If it is non-local, then it can. That is the only way to make it compatible with Bell's Theorem, since he is requiring realism. Obviously, entanglement experiments support the idea that distant particles share a common wave function, and therefore they cannot have both predetermined properties and independence. At the time Popper's ideas were being written, this area was being revolutionized and there is no shortage of confirmation at this point.

 

[kote]

Dr. Chinese, I am personally also more drawn to the Bohmian interpretation but I'm not sure that Bohm and Popper/Lande are entirely incompatible. Bohm's "implicate order" may be likened to Popper's "propensity fields," which he described as real but not physical - just as Bohm did the implicate order. Popper did in fact make much of entanglement, calling in the early 1980s after the Aspect experiments for a broad-scale revision of relativity and quantum theory - on the former claiming that the Aspect experiments undermined the idea of relative simultaneity, which is the basis for the entire edifice of relativity theory. Could you flesh out why you think Popper's theory can't deal with entanglement?

Tam, have you read Bohm's concept of active information? It sheds some light on what the eventual implications of the "Bohmian Interpretation" are.

Bohm suggests that there is an infinite recursion of physical properties reducing to mental properties reducing to physical properties etc. This seems to be the only way for him to explain nonlocal information transfer in a realist framework.

After all of his efforts to create a deterministic realist theory, Bohm writes that there is a “deeper reality … beyond either mind or matter, both of which are only aspects that serve as terms for analysis.”

I point this out because popular literature seems to have ignored Bohm for the past 30 years, and generally presents only his incomplete 1950s view. I was certainly surprised to read his more recent thoughts.

Bohm, D. (1990) `A New Theory of the Relationship of Mind and Matter', Philosophical Psychology 3: 271--86.

http://evans-experientialism.freewebspace.com/bohmphysics.htm

^ Try finding that or similar papers referenced anywhere on anything related to Bohm's interpretation.

 

[Tam Hunt]

Thanks Kote, I have read that article by Bohm and I also recently finished his Wholeness and the Implicate Order. I am drawn to Bohm's interpretation and am glad to see that physicists in this forum at least are again discussing his ideas.

 

[Tam Hunt]

Dr. Chinese, have you read about the Salart experiment from last year, finding that the non-local signal traveled at least 10,000 times the speed of light? What do most working physicists think of this experiment? I've found, surprisingly, almost no discussion of this experiment online (I don't have access to physics journals as I am not a working physicist).

 

[DrChinese]

Dr. Chinese, have you read about the Salart experiment from last year, finding that the non-local signal traveled at least 10,000 times the speed of light? What do most working physicists think of this experiment? I've found, surprisingly, almost no discussion of this experiment online (I don't have access to physics journals as I am not a working physicist).

Yes I am familiar with this experiment. It conclusion essentially states that IF there is a superluminal influence, THEN it must occur at >10,000c. It does not, however, require a superluminal influence.

In fact, there are some superluminal theories that are excluded by this result (as it tends to refute the notion of an absolute reference frame, which is a part of some variants). However, it is generally considered as to NOT refute standard Bohmian concepts (per Demystifier who generally does support an absolute reference frame, IIRC).

 

[Tam Hunt]

Dr. Chinese, can you point me to additional info/articles on the Salart experiment and others like it? I'd like to follow up on your points but don't have access to the actual paper by Salart.

 

[f95toli]

Dr. Chinese, have you read about the Salart experiment from last year, finding that the non-local signal traveled at least 10,000 times the speed of light? What do most working physicists think of this experiment? I've found, surprisingly, almost no discussion of this experiment online (I don't have access to physics journals as I am not a working physicist).

The reason why it is not being discussed is that the result was exactly what one would expect from conventional QM. The experiment was a test of QM; it did not give us any new information as such.
There are lots of experiments being conducted to test various fundamental theories, either aspects of QM or GR.
Now, this is important work but unless someone gets a result that is NOT what one would expect (as in the fine-structure experiments a couple of years ago) these experiment don't
get much attention.

 

[Dale]

Heisenberg's uncertainty formulae are not actual limits on the precision of our knowledge,... have a real and precise position and momentum. ... in Popper's interpretation there is a real particle, with defined position and momentum, ... fields are properties of a given experimental arrangement, not of the particles that are the object of study.

I find these comments pretty amusing and hypocritical coming from the prince of "falsifiability". How could any of these statements be experimentally falsified?

 

[DrChinese]

Dr. Chinese, can you point me to additional info/articles on the Salart experiment and others like it? I'd like to follow up on your points but don't have access to the actual paper by Salart.

Sure, here it is: http://arxiv.org/abs/0808.3316

 

[DrChinese]

I find these comments pretty amusing and hypocritical coming from the prince of "falsifiability". How could any of these statements be experimentally falsified?

And yet I actually think they have been. At least in local theories. I think the whole thrust of Bell and after is that you must give up one or the other cherished notions: realism or locality. Popper's referenced work doesn't seem to do either, so it won't go too far in this area.

 

[kote]

And yet I actually think they have been. At least in local theories. I think the whole thrust of Bell and after is that you must give up one or the other cherished notions: realism or locality. Popper's referenced work doesn't seem to do either, so it won't go too far in this area.

I won't go into it here, but that supposed choice between realism and locality always gets me :). Presented as such, "realism" seems like the obvious choice while locality is just an abstract concept. What is realism without locality though? A nonlocal realism won't adhere to classical notions of causality, it won't have classical spatiotemporal or wave properties as its basic features, and it won't adhere to relativity.

I agree that giving up either is huge, and QM totally falsifies all notions of reality that are anything like the classical mechanized paradigm.

 

[Demystifier]

(per Demystifier who generally does support an absolute reference frame, IIRC).

Well, yes and know. I prefer theories without an absolute reference frame, if possible. A large part of my research in Bohmian mechanics consists in attempts to formulate Bohmian mechanics without an absolute reference frame. Still, a possibility that an absolute reference frame exists also makes a lot of sense to me.

 

[Demystifier]

What is realism without locality though?

Bohmian mechanics suggests that realism is still local in the sense that the world consists of local particles, but nonlocal in the sense that forces between them "propagate" instantaneously.

A nonlocal realism won't adhere to classical notions of causality, it won't have classical spatiotemporal or wave properties as its basic features, and it won't adhere to relativity.

And yet, all these classical features emerge as approximations in a suitable limit. By the way, nonlocality IS compatible with relativity:
http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]

 

[Tam Hunt]

The reason why it is not being discussed is that the result was exactly what one would expect from conventional QM. The experiment was a test of QM; it did not give us any new information as such.
There are lots of experiments being conducted to test various fundamental theories, either aspects of QM or GR.
Now, this is important work but unless someone gets a result that is NOT what one would expect (as in the fine-structure experiments a couple of years ago) these experiment don't
get much attention.

f95: isn't the Salart experiment strong data in favor of non-locality, contradicting the no supraluminal signaling limitation of special relativity? Of course, the Aspect experiments established this more than two decades ago, but this truth seems to not have percolated into the prevailing physical paradigm of our era.

 

[DrChinese]

f95: isn't the Salart experiment strong data in favor of non-locality, contradicting the no supraluminal signaling limitation of special relativity?

That is not what the experiment is about, as the issue was whether there is a preferred reference frame and finite FTL propagation. Traditional Bell tests cannot set very high lower limits on the speed of FTL influences (if they exist). You might expect about 2c or so as the top you could achieve in this fashion. So clearly, setting the lower limit at 10,000c is a signficant improvement.

You can easily convince yourself that either realism or locality must be false due to Bell; but it is easier to reject locality if you are trying to picture a physical mechanism. Not that a physical picture is necessary. On the other hand: Personally, I think it comes back to the HUP. If we could visualize the physical mechanism that it operates by, then it would be a lot easier to visualize rejecting realism (with the objective that locality can remain inteact). So in my book, both locality and the HUP should be equally fundamental; although I recognize that this view is not strictly demanded by the facts. Demystifier makes a lot of good points about the other side.

 

[kote]

Bohmian mechanics suggests that realism is still local in the sense that the world consists of local particles, but nonlocal in the sense that forces between them "propagate" instantaneously.And yet, all these classical features emerge as approximations in a suitable limit. By the way, nonlocality IS compatible with relativity:
http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]

Demystifier,

The paper you cite is very critically flawed. It relies on an earlier paper, "Relativistic Bohmian interpretation of quantum mechanics," by the same author. This previous paper more clearly outlines its assumptions. One of these assumptions reads:

"According to the Bohmian interpretation, all QM uncertainties emerge from the ignorance of the actual initial particle position x(t0)."

This statement is false. Bohmian mechanics makes no such assertion. EPR type experiments have proven that any supposed hidden variables cannot be classical variables. If we were just uncertain of the initial classical variables in these experiments then the measured (and QM predicted) probabilities would match classically predicted probability densities. They don't. That's why we have a quantum paradox to begin with.

Special relativity is a statement of locality. Relativity is locality. You can't deny one without denying the other.

 

[Dale]

Special relativity is a statement of locality. Relativity is locality.

No, special relativity is a statement of symmetry. As long as your theory has Poincare symmetry it is relativistic. You can certainly think of non-local theories with Poincare symmetry.

 

[kote]

Tam... you've gotten at the core of the interpretational argument over QM here. You, as Bohm did, seem to be taking as fundamental that there are real deterministic laws governing the natural world. And, as Bohm did, this leads to a situation where basic reality exists out there somewhere (your "ether") but we can have no knowledge of its basic properties. All we can know is that it's out there and it's causing all of these phenomena that we are observing. The price to pay here is that for all the realism about the theory, in principle, you can't ascribe basic reality to anything at all. Particles aren't real at a basic level. Waves aren't real at a basic level. Nothing that we can ever describe is real at a basic level.

Bohr's interpretation (and others) make an alternate assumption. Instead of taking deterministic natural laws as real, they propose that, if we inherently can't know anything about the forces and properties at play beneath the classical level, we shouldn't call any of that stuff real. Bohr's primary premise is that classical objects and properties are basic and real. This allows him to say that location is real, mass is real, etc. It also allows him to restore properties previously demoted to the "extrinsic" level to the same level of reality as location and mass. Color and sound are just as real as mass and velocity. The price to pay for this basic assumption and the resulting interpretation is that the basic properties can't exist persistently and objectively. There are no properties in a vacuum. Momentum only exists during collisions and not between collisions. When a tree falls in the forest there is no sound if no one is there to hear it :).

Both classes of interpretation are equally valid. It comes down to the semantics of reality. If only objective properties are real, as per Bohm, we end up with epistemological instrumentalism where reality is inherently inaccessible and in the "ether." If the objects of our perception are real then we can ascribe reality to all of the things that we would like to naively, but we are left without separable objective properties.

 

[yossell]

One of these assumptions reads:

"According to the Bohmian interpretation, all QM uncertainties emerge from the ignorance of the actual initial particle position x(t0)."

This statement is false. Bohmian mechanics makes no such assertion.

I am baffled. Are you sure of this? I thought (standard) Bohmian mechanics made precisely such an assertion. As I understood it, Bohmian mechanics is deterministic - but both the wave and the particles evolve in a deterministic fashion.

yossell

 

[Dale]

It comes down to the semantics of reality.

I agree completely. Semantic arguments are notoriously difficult to resolve. I prefer to learn all of the different interpretations and use one when it is useful and another when that one is useful, and not get tied down in picking just one interpretation.

 

[yossell]

No, special relativity is a statement of symmetry. As long as your theory has Poincare symmetry it is relativistic. You can certainly think of non-local theories with Poincare symmetry.

Hi Dale,

what kinds of theories did you have in mind here? I thought that locality arose fairly naturally from relativity. I take non-local to be something like an instantaneous action across a finite spatially separated region. Such an action would be...well, instantaneous i.e. there would involve an absolute notion of simultaneity, in tension with most formulations of relativity.

I can see perhaps some wiggle room. For instance, if relativity is the statement that the basic laws of nature are invariant across inertial frames, and if it turns out that the basic laws are probabilistic, then there's room for individual processes to be non-local, although, statistically, in the long run, the world behaves locally. Was this the kind of thing you had in mind? Or is there something simpler and more obvious that I'm missing?

yossell

 

[DrChinese]

Demystifier,

The paper you cite is very critically flawed. It relies on an earlier paper, "Relativistic Bohmian interpretation of quantum mechanics," by the same author. This previous paper more clearly outlines its assumptions. One of these assumptions reads:

"According to the Bohmian interpretation, all QM uncertainties emerge from the ignorance of the actual initial particle position x(t0)."

This statement is false. Bohmian mechanics makes no such assertion. EPR type experiments have proven that any supposed hidden variables cannot be classical variables. If we were just uncertain of the initial classical variables in these experiments then the measured (and QM predicted) probabilities would match classically predicted probability densities. They don't. That's why we have a quantum paradox to begin with.

Special relativity is a statement of locality. Relativity is locality. You can't deny one without denying the other.

Bohmian theory provides deterministic solutions; but due to the Quantum Equilibrium Hypothesis, initial particle positions are distributed according to a psi^2 spread. That is why outcomes can never be predicted. See for example: What you always wanted to know about Bohmian mechanics but were afraid to ask.

Further, you will find Demystifier quite knowledgeable about BI, his specialty is deep BI theory - especially how it relates to SR. Your comments about Nikolic's papers similarly off (not surprisingly as you will learn). Bohmian theory is manifestly non-local, and it is considered viable at this time. However, there are a few variants of Bohmian/dBB out there; some have a preferred frame and some do not. There are a number of issues with both sides of this question that are fairly technical (certainly beyond me).

Lastly, EPR experiments do NOT conclude that hidden variables cannot be classical. These experiments rather show that they cannot be both classical AND local.

 

[Dale]

Such an action would be...well, instantaneous i.e. there would involve an absolute notion of simultaneity

Not necessarily. You can easily have any two of FTL, relativity, and causality. An instantaneous action may be relativistic, in which case it would violate causality in some reference frames.

 

[kote]

I am baffled. Are you sure of this? I thought (standard) Bohmian mechanics made precisely such an assertion. As I understood it, Bohmian mechanics is deterministic - but both the wave and the particles evolve in a deterministic fashion.

yossell

Absolutely. Any hidden variables theory that posits classical spatiotemporal properties as its hidden variables has been falsified by experimentation and contradicts the predictions of QM. Take spin, for example. We are only able to measure spin as being +1 or -1. Try to visualize an electron as a globe with its spin pointing in the direction of the "north pole." One way to explain the +1 or -1 result would be to say force is quantized, and as long as the spin / north pole is more in the up direction than the down direction, it will experience a force of +1.

Due to conservation laws, when you fire two entangled electrons off in opposite directions, the one fired in the opposite direction will have its spin correspond to the south pole. It will measure -1.

Now, as the experiment goes, you can rotate the Stern-Gerlach device on the back side so it isn't directly aligned with the one in front. Rotate it 120 degrees. Classical probability demands that, in this setup, there is a 1/3rd chance of measuring +1 on the second device if you're measured +1 on the first. One third of the rotated "up" hemisphere is aligned with one third of the original "up" hemisphere.

This one-third relation holds for any definition of spin that gives it a definite, persistent, 2 or 3 dimensional direction.

Allowing the amplitude of the spin to change so that its vector may be found anywhere in the electron sphere does not change the results. Constricting the vector to the two dimensions perpendicular to the path of the electron does not change the one-third relationship. Whether the overlap is in the volume of the hemispheres, the area, the circumference... it makes no difference. Any definite geometric definition for spin, even a hidden definition, results in a prediction of a one-third probability for measuring the same reading on both devices.

Quantum mechanics predicts 1/4. Experiments show a 1/4 correlation. No classical definition of spin, regardless of how fuzzy or indefinite it is, is consistent with reality. Spin cannot be defined spatiotemporally.

If we still hold to realism at this point and claim that spin is real, then basic reality is proven to not be found in classical space-time. This is the quantum paradox that destroys classical notions of reality regardless of the metaphysical interpretive framework.

Similar results come using polarization and other properties.

 

[kote]

Bohmian theory provides deterministic solutions; but due to the Quantum Equilibrium Hypothesis, initial particle positions are distributed according to a psi^2 spread. That is why outcomes can never be predicted. See for example: What you always wanted to know about Bohmian mechanics but were afraid to ask.

Further, you will find Demystifier quite knowledgeable about BI, his specialty is deep BI theory - especially how it relates to SR. Your comments about Nikolic's papers similarly off (not surprisingly as you will learn). Bohmian theory is manifestly non-local, and it is considered viable at this time. However, there are a few variants of Bohmian/dBB out there; some have a preferred frame and some do not. There are a number of issues with both sides of this question that are fairly technical (certainly beyond me).

Lastly, EPR experiments do NOT conclude that hidden variables cannot be classical. These experiments rather show that they cannot be both classical AND local.

DrChinese,

I agree that Bohm's view is viable. I view it as self-consistent, and as such, it can only be falsified with a falsification of QM itself. My previous comment explains my objection to the the possibility of classical/spatiotemporal hidden variables. As for your final point, classical objects and properties behave locally. To deny locality is to deny core aspects of the classical view. It sounds like we'll just have to disagree on that! :)

 

[kote]

See for example: What you always wanted to know about Bohmian mechanics but were afraid to ask.

Thanks for the link. Interesting article. It looks consistent to me, and I appreciate the quote by a philosopher :). I find it especially interesting that this description of BI avoids the falsified causal implications of classical properties by simply denying the existence of any classical properties with causal implications.

"Just as psi is no classical field, the Bohmian particles are no classical particles. i.e., they are no bearers of properties other than position. ... Agreed, this is a radical departure from the classical particle concept."

Doesn't personally do it for me, but as far as I can tell it's perfectly viable and as provable as other self-consistent theories. I'll save the semantic arguments for a different forum (they aren't as interesting anyways).

 

[kote]

Not necessarily. You can easily have any two of FTL, relativity, and causality. An instantaneous action may be relativistic, in which case it would violate causality in some reference frames.

DaleSpam,

I'm glad you brought this up. It shows our differences in assumptions. I would argue that relativity and locality are synthetic propositions while causality is an analytic truth. That a cause must precede its effect is guaranteed by the definitions of the words cause and effect, putting it on the same level as 1+1=2.

A theory can still comply with the tautological truth of causality by redefining time - by redefining what it means for one event to precede another. Doing this, however, gives you a definition of time inconsistent with time in relativity.

So I have been assuming that, at least without throwing out relativity, causality must be true. Without this assumption I would agree with all of your previous statements.

 

[DrChinese]

... I would argue that relativity and locality are synthetic propositions while causality is an analytic truth. That a cause must precede its effect is guaranteed by the definitions of the words cause and effect, putting it on the same level as 1+1=2.

A theory can still comply with the tautological truth of causality by redefining time - by redefining what it means for one event to precede another...

I would agree that assuming causality is tautological. And the evidence is fully consistent with the ideas that a) there are NO causes; or b) the future influences the past.

 

[Demystifier]

Special relativity is a statement of locality. Relativity is locality.

No it isn't. If it were, then we would not have two different words for the same thing.

 

[Demystifier]

And the evidence is fully consistent with the ideas that a) there are NO causes; or b) the future influences the past.

I would say that both a) and b) are true. Let me explain.

What does it mean that A is cause of B? It means a logical relation
A -> B
i.e., A IMPLIES B.
But what if both
A -> B
and
B -> A
are true?
Should we say that then A is a cause of B and B is a cause A? I don't think so. It's better to say that the notion of cause and consequence do not have any fundamental meaning. (They have only meaning on an effective macroscopic level, due to the second "law" of thermodynamics.)