I Are there any accepted relativistic interpretations of quantum mechanics?

[pines-demon]

From the few interpretations of quantum mechanics that I know, let's say:

• Copenhagen
• Many Worlds (MWI)
• Bohmian mechanics
• Superdeterminism
• Retrocausality/transactional
• Objective-collapse
• Qbism*
• Consistent histories*

I believe the only one that accepts a relativistic version in Copenhagen interpretation and only because it is completely agnostic to many points. Bohmian mechanics has always been criticized for not being field-like or and unable to be relativistic. Per Measurements in QFT I understand that MWI does not have an accepted relativistic version. I would argue that Superdeterminism and objective-collapse are more like ingredients of interpretation and barely count for relativistic concerns. And retrocausality just throws causality in the drain. And the others with a * I do not know even know what they mean or how they solve anything.

Anyway is there an interpretation in quantum mechanics with an accepted realtivistic formulation?

 

[Morbert]

Consistent histories is readily applicable to any quantum theory, where a "quantum theory" is a theory whose C*-algebra of observables is non commutative. Under consistent histories, complementary "classical" boolean lattices are constructed from this algebra, and hence frameworks for constructing reliable logical propositions and inferences about quantum systems. In a sense, the name "consistent histories" buries the lede. It should be called something like complementary lattices interpretation.

 

[pines-demon]

Consistent histories is readily applicable to any quantum theory, where a "quantum theory" is a theory whose C*-algebra of observables is non commutative. Under consistent histories, complementary "classical" boolean lattices are constructed from this algebra, and hence frameworks for constructing reliable logical propositions and inferences about quantum systems. In a sense, the name "consistent histories" buries the lede. It should be called something like complementary lattices interpretation.

Could you recommend any introduction to this interpretation?

 

[Morbert]

Could you recommend any introduction to this interpretation?

"Classical Equations for Quantum Systems" by James Hartle and Murray Gell-Mann is a good paper.

"Understanding Quantum Mechanics" by Roland Omnes and "Consistent Quantum Theory" by Robert Griffith are good books.

[edit] - The paper probably isn't good as an introduction. Better to start with the books and move to the paper after.

 

[Demystifier]

Bohmian mechanics has always been criticized for not being field-like or and unable to be relativistic.

For a response to such critiques see my https://arxiv.org/abs/2205.05986

 

[Fra]

• Qbism*

...
And the others with a * I do not know even know what they mean or how they solve anything.

Anyway is there an interpretation in quantum mechanics with an accepted realtivistic formulation?

IMO, in an observer centered view like qbism, I would take "relativity" to be a statement about the relations between different observers/agents; which is indirectly a statement about the "environment" or embedding of the quantum system, from where observations are made.

Ie. the "relativisitic formulation" is not so much a statement about the quantum system, as it is about the relations within the equivalence class of "descriptions of the quantum system", from the perspective of a set of "inertial observers".

Weird paradoxal things still happen when you try to make this "observer structure" part of the quantum system (just like you try to make "macroscopic measuremen devices" part of a quantum system. But this I think is an limitation with the theory, and I dont' see how a pure interpretation can solve it.

/Fredrik

 

[RUTA]

From the few interpretations of quantum mechanics that I know, let's say:

• Copenhagen
• Many Worlds (MWI)
• Bohmian mechanics
• Superdeterminism
• Retrocausality/transactional
• Objective-collapse
• Qbism*
• Consistent histories*

I believe the only one that accepts a relativistic version in Copenhagen interpretation and only because it is completely agnostic to many points. Bohmian mechanics has always been criticized for not being field-like or and unable to be relativistic. Per Measurements in QFT I understand that MWI does not have an accepted relativistic version. I would argue that Superdeterminism and objective-collapse are more like ingredients of interpretation and barely count for relativistic concerns. And retrocausality just throws causality in the drain. And the others with a * I do not know even know what they mean or how they solve anything.

Anyway is there an interpretation in quantum mechanics with an accepted realtivistic formulation?

The spacetime distribution of quantum events per the Hilbert space (kinematics) of QM is perfectly compatible with the Minkowski spacetime (M4 kinematics) of SR, as long as one does not add non-Lorentz-invariant dynamics in an attempt to account constructively for spacelike correlated quantum events in time-ordered fashion. This holds even though the time evolution of the state vector in a fixed-dimensional Hilbert space (dynamics) is governed by Schrodinger's equation which is not Lorentz invariant, because the kinematics is only concerned with the distribution of quantum outcomes in M4. Schrodinger's equation is simply the low energy approximation of the Lorentz-invariant Klein-Gordon equation of quantum field theory, which accounts for distributions in M4 requiring Hilbert spaces of many different dimensions (Fock space).

 

[gentzen]

Schrodinger's equation is simply the low energy approximation of the Lorentz-invariant Klein-Gordon equation of quantum field theory

This is simply nonsense.

 

[RUTA]

This is simply nonsense.

Zee, A. (2003). Quantum Field Theory in a Nutshell. Princeton University Press, Princeton, p. 173

 

[gentzen]

Zee, A. (2003). Quantum Field Theory in a Nutshell. Princeton University Press, Princeton, p. 173

I guess you are talking about a section that starts with "For clarity consider first the relativistic Klein-Gordon
equation $$(\partial^2 + m^2)\Phi = 0 \qquad (2)$$ for a free scalar field. A mode with energy E=..." and ends with "Dropping the term $(\partial^2/\partial t^2)\varphi$ as small compared to $−2im(\partial/\partial t)\varphi$, we find Schrödinger’s equation, as we had better: ...(3)"
What you get here is a Schrödinger equation for a single particle. But didn't you start with an equation describing an entire field, i.e. potentially multiple particles? That is no surprise in the book, because the derivation focused on a single "mode with energy E=...". So the book is fine from my perspective.

But your claim is nonsense, because the Klein-Gordon equation describes bosons, while the nonrelativistic Schrödinger equation is used for both bosons and fermions. A derivation which works fine for the case of a single particle doesn't necessarily generalize for the case of multiple particles!

 

[Demystifier]

because the Klein-Gordon equation describes bosons,

That's not necessarily true. A function $\psi(x)$ that satisfies Dirac equation, satisfies also the Klein-Gordon equation.

 

[gentzen]

That's not necessarily true. A function $\psi(x)$ that satisfies Dirac equation, satisfies also the Klein-Gordon equation.

You mean I should have written "because the Lorentz-invariant Klein-Gordon equation of quantum field theory describes bosons" instead?
Also, your statement still seems to talk about the single particle case, so it doesn't yet invalidate my statement that "A derivation which works fine for the case of a single particle doesn't necessarily generalize for the case of multiple particles!". More generally, I hope that despite of your criticism of details of my post, you still agree that the statement about Schrödinger's equation which I called nonsense is at least very misleading.

 

[Demystifier]

Also, your statement still seems to talk about the single particle case

There are also Dirac and Klein-Gordon equations for many-particle states. See e.g. my https://arxiv.org/abs/1205.1992 Sec. 8.3.3.

 

[RUTA]

I guess you are talking about a section that starts with "For clarity consider first the relativistic Klein-Gordon
equation $$(\partial^2 + m^2)\Phi = 0 \qquad (2)$$ for a free scalar field. A mode with energy E=..." and ends with "Dropping the term $(\partial^2/\partial t^2)\varphi$ as small compared to $−2im(\partial/\partial t)\varphi$, we find Schrödinger’s equation, as we had better: ...(3)"
What you get here is a Schrödinger equation for a single particle. But didn't you start with an equation describing an entire field, i.e. potentially multiple particles? That is no surprise in the book, because the derivation focused on a single "mode with energy E=...". So the book is fine from my perspective.

But your claim is nonsense, because the Klein-Gordon equation describes bosons, while the nonrelativistic Schrödinger equation is used for both bosons and fermions. A derivation which works fine for the case of a single particle doesn't necessarily generalize for the case of multiple particles!

You've Zee's point. He has the general prescription for taking "the nonrelativistic limit of a quantum field theory" at the bottom of p. 172 so that you obtain the SE from the KG equation ("as we had better"). A QM Hilbert space can represent more than one particle, yet it is surely the case that the SE governs the time evolution of the state vector in Hilbert space. Zee is simply showing you how to get the relevant nonrelativistic diffusion equation from the relevant relativisitic wave equation, since this it is the Hamiltonian for this equation that dictates the evolution in a fixed-dimensional Hilbert space, i.e., if you start with 2 particles you always have 2 particles. That's QM, it's the nonrelativistic limit of QFT where you can start with 2 particles and end up with many more than 2 (Hilbert space --> Fock space). Consider the alternative hypothesis, i.e., QM isn't the nonrelativistic limit of QFT, but some other theory is. Then you'd expect so see some deviation between QM predictions and experimental data where both QM and this hypothetical alternative nonrelativistic limit of QFT conflict but are expected to hold. I don't know of any such deviations between experimental data and QM.

Likewise, people who think QM and SR are "incompatible" (e.g., "On the Incompatibility of Special Relativity and Quantum Mechanics" https://arxiv.org/pdf/1704.02587.pdf) can't possible be talking about the theories themselves. Both theories work beautifully in their realms of applicability. Quantum entanglement is usually blamed for this supposed incompatibility between the theories, but physicists do not believe the experimental evidence in accord with QM refutes SR. So, it's not the physics that is problematic, it's the physicists and philosophers who have preconceived notions of reality that don't allow them to understand the empirical evidence in support of the theories. The problem stems from trying to account dynamically/constructively for the QM correlations between spacelike related measurement outcomes that violate Bell inequalities. Doing so necessarily violates locality, statistical independence, intersubjective agreement, or the uniqueness of experimental outcomes. QM does not contain such a causal mechanism, so it doesn't necessitate the violation of any of those things.

I could say a lot more, but I don't have time. My colleagues and I have a book coming out this summer with Oxford UP titled, "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" where we go into great detail for the general reader on how to understand entanglement in principle fashion so as to avoid these undesirable consequences of "constructive efforts." I'll leave it there.

 

[gentzen]

I could say a lot more, but I don't have time. My colleagues and I have a book coming out this summer with Oxford UP titled, "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" where we go into great detail for the general reader on how to understand entanglement in principle fashion so as to avoid these undesirable consequences of "constructive efforts." I'll leave it there.

Fine, you don't need to say much. Just clearly replace the statement

Schrodinger's equation is simply the low energy approximation of the Lorentz-invariant Klein-Gordon equation of quantum field theory

by something which is less disparaging towards nonrelativistic QM. As I said, the Klein-Gordon equation only applies to bosons, and this is not a limitation of nonrelativistic QM. It is true that nonrelativistic QM has trouble creating or destroying particles, and hence has a hard time with photons, because they are massless.

Please also see my point. I have invested huge efforts to understand nonrelativistic QM good enough to be able to somehow use it in my daily job. I have some knowledge of QFT, but far less than of QM. It is fine for me to read your references to Zee, or Demystifier's paper. But the way this discussion here went feels very bad to me.

 

[Morbert]

As an aside: An interesting paper (that I unfortunately cannot find a preprint of )

They present the Schroedinger equation in QFT as $$\sum_{k=1}^n \frac{\partial}{\partial x_k^0}\psi(A|x_1,\dots,x_n) = H\psi(A|x_1,\dots,x_n)$$where the Hilbert space is a linear space of wave functionals and $$\psi(A|x_1,\dots,x_n) =N \int D\left[\phi\right]\phi(x_1)\dots\phi(x_n)e^{-S\left[\phi\right]}$$

 

[PeterDonis]

the way this discussion here went feels very bad to me.

When you use the word "nonsense" to describe someone else's post, you should expect to feel bad. It would have been better to dial back your response to something like asking for a reference. Which you got anyway.

 

[A. Neumaier]

It is true that nonrelativistic QM has trouble creating or destroying particles, and hence has a hard time with photons, because they are massless.

Standard QM can handle a finite number of free relativistic particles (including photons) easily in the momentum picture!

The free Hamiltonian for a single particle of mass $m\ge 0$ and spin $s$ is $H_0=\sqrt{p^2+m^2}$ acting on the Hilbert space $L^2(R^3,C^{2s+1})$ - except in the massless spin $s\ge 1$ case, where the Hilbert space is the subspace of helicity $\pm s$ states. Thus for photons ($m=0,s=1$), $\psi$ must satisfy $p\cdot\psi(p)=0$.

In a finite-dimensional truncated Fock space one can also handle several free particles and their interaction, incuding their creation and annihilation unless the interaction allows the creation of too many particles. Thus the production of soft photons (Bremsstrahlung) cannot be modeled, but many other creation and annihilation processes can!

Indeed, quantum optics routinely and successfully uses truncated Fock spaces for the approximate description of processes involving photons.

 

[gentzen]

When you use the word "nonsense" to describe someone else's post, you should expect to feel bad. It would have been better to dial back your response to something like asking for a reference. Which you got anyway.

I didn't describe his post as nonsense. I objected to a specific statement. Then I got a reference as reply, which explains where that statement came from, but basically just confirms that the statement as made is objectionable. Then I explained in detail why the statement is still objectionable, despite the reference. So far so good, nothing that would feel bad to me.

But then the wiggling and objections started, picking on details and giving the false impressions as if those details would invalidate my points. I don't want PF to become the original source for the statement that "Schrödinger's equation is simply the low energy approximation of the Lorentz-invariant Klein-Gordon equation of quantum field theory", backed up by ... I don't want this, because this statement is disparaging towards Schrödinger's equation, and misleading.

Edit: And the word "nonsense" is my reaction to the word "simple". I find it unbelievably condescending to use words like "of course", "simple", "..." in the context of stuff related to QFT.

 

[PeterDonis]

I didn't describe his post as nonsense. I objected to a specific statement.

You're quibbling. You used the word "nonsense".

the word "nonsense" is my reaction to the word "simple". I find it unbelievably condescending to use words like "of course", "simple", "..." in the context of stuff related to QFT.

And that's fine if that's your reaction. But if you're going to go the route of expressing that reaction in a public post, don't complain later that the way the discussion went "feels bad" to you. You used the word "nonsense", so own it. If you don't like the way the discussion went as a result, then next time you might want to choose a more moderate response, as I said.

 

[PeterDonis]

But then the wiggling and objections started, picking on details and giving the false impressions as if those details would invalidate my points. I don't want PF to become the original source for the statement that "Schrödinger's equation is simply the low energy approximation of the Lorentz-invariant Klein-Gordon equation of quantum field theory", backed up by ... I don't want this, because this statement is disparaging towards Schrödinger's equation, and misleading.

It should be evident to you from the discussion that others posting in this thread do not share your viewpoint here. I personally can't even make sense of your claim that the statement is "disparaging towards Schrodinger's equation"--how can you "disparage" a physics equation? Are you afraid its feelings will get hurt?

As far as the statement in Zee's book, I read that book years ago and saw no issue with it. So my general reaction to your objections is similar to that of other posters in the thread.

 

[bhobba]

To throw the cat among the pigeons, does QFT require any interpretation over and above the principles of QM?

Weinberg is famous for his view (he calls it a folk theorem) that any theory looks like a QFT at large enough distances and the EFT view of QFT
https://philarchive.org/archive/CARTQF-5

If that is true, what is there to interpret?

That then raises the issue of how natural an interpretation is when applied to the QFT subset of QM.

Also, there is the issue, likely requiring a separate thread, of what are the principles of QM? Most I have seen (Ballentine is an exception) include the Schrodinger equation, so those are ruled out.

Thanks
Bill

 

[physika]

From the few interpretations of quantum mechanics that I know, let's say:

• Copenhagen
• Many Worlds (MWI)
• Bohmian mechanics
• Superdeterminism
• Retrocausality/transactional
• Objective-collapse
• Qbism*
• Consistent histories*

Objective Collapse is not an interpretation, it is a theory by is own.


......

 

[PeterDonis]

Objective Collapse is not an interpretation, it is a theory by is own.......

Some versions are, such as the GRW stochastic collapse model, since they explicitly change the math. But I'm not sure all interpretations that call themselves "objective collapse" do that.

 

[gentzen]

Some versions are, such as the GRW stochastic collapse model, since they explicitly change the math. But I'm not sure all interpretations that call themselves "objective collapse" do that.

The only such "objective-collapse" interpretation I am aware of (which doesn't change the math) is the infamous "consciousness causes collapse" interpretation (which should not be called von Neumann–Wigner interpretation despite wikipedia, because von Neumann and Wigner described something else). I would argue that this should not deter us from using "objective-collapse theory" just like wikipedia and SEP, referring specifically to those collapse interpretations that do change the math.

So back to @physika's point of whether using the word "interpretation" for those theories is OK. Given that wikipedia and SEP take care not to call them interpretations, it feels like a good idea in general to follow that practice. But this practice also includes the Penrose interpretation. It seems to be a question of the effort and disruption it would cause, to insist to never refer to such theories using the word "interpretation".

 

[physika]

Some versions are, such as the GRW stochastic collapse model, since they explicitly change the math. But I'm not sure all interpretations that call themselves "objective collapse" do that.

(Ghirardi, Rimini & Weber)
As Ghirardi says

"Collapse Theories qualify themselves as rival theories of quantum mechanics and one can easily identify some of their physical implications which, in principle, would allow crucial tests discriminating between the two"

https://plato.stanford.edu/Entries/qm-collapse/

 

[PeterDonis]

As Ghirardi says

Of course he's going to say that, since it is true for his "objective collapse" interpretation.

 

[physika]

"tests discriminating between the two"

https://plato.stanford.edu/Entries/qm-collapse/

Tests will tell.

 

[gentzen]

To throw the cat among the pigeons, does QFT require any interpretation over and above the principles of QM?
[...]
That then raises the issue of how natural an interpretation is when applied to the QFT subset of QM.

Peter Woit posted an interesting link on February 14, 2024, which might be relevant:

While trying to figure out how best to pass from QM to QFT, I’ve kept coming across various aspects of this that I’ve always found confusing, never seen a good explanation of. Today I ran across a wonderful article by Thanu Padmanabhan, who I knew about just because of his very good introductory book on QFT, Quantum Field Theory: The why, what and how. The article is called “Obtaining the Non-relativistic Quantum Mechanics from Quantum Field Theory: Issues, Folklores and Facts” and subtitled “What happens to the anti-particles when you take the non-relativistic limit of QFT?” It contains a lot of very clear discussion of issues that come up when you try and think about the QM/QFT relationship, a sort of thing I haven’t seen anywhere else.

Especially the following quote from https://arxiv.org/abs/1712.06605 ("Obtaining the Non-relativistic Quantum Mechanics from Quantum Field Theory: Issues, Folklores and Facts" by T. Padmanabhan)

The dichotomy of description between NRQM and QFT does not originate just from the square root in the Hamiltonian or from the demand of Lorentz invariance, as it is sometimes claimed. The real difficulty has its origin in the necessary existence of antiparticles to ensure a particular notion of relativistic causality. Because of these conceptual issues, it turns out that one cannot, in fact, obtain some of the popular descriptions of NRQM by any sensible limiting procedure applied to QFT. To obtain NRQM from QFT in a seamless manner, it is necessary to work with NRQM expressed in a language closer to that of QFT. This fact has several implications, especially for the operational notion of space coordinates in quantum theory.

hints at similar issues as the following quote from https://arxiv.org/abs/1205.1992 ("Relativistic Quantum Mechanics and Quantum Field Theory" by H. Nikolic), a link posted by Demystifier earlier in this thread:

In our quest towards relativistic Bohmian mechanics, as a byproduct we realize that even non-Bohmian relativistic QM and QFT should be first made “more relativistic” than they are in the usual formulation, i.e., that time and space should be treated more symmetrically. First, the usual single-time wave function should be generalized to the many-time wave function, such that each particle has its own spacetime coordinate. Second, $\psi^2$ should be reinterpreted as a probability density in spacetime, rather than that in space.

 

[A. Neumaier]

Peter Woit posted an interesting link on February 14, 2024, which might be relevant:

Especially the following quote from https://arxiv.org/abs/1712.06605 ("Obtaining the Non-relativistic Quantum Mechanics from Quantum Field Theory: Issues, Folklores and Facts" by T. Padmanabhan)

You forgot to mention the main result (substantiated in Section 6) of the paper:

the transition from QFT to NRQM is not possible if your aim is to reproduce many of the conventional descriptions of NRQM. Towards the end of the paper, I will describe how this can be achieved using one specific formulation of NRQM.

This means that - in contrast to what you suggest - when properly done, there are no issues at all with the nonrelativistic limit of QFT!

 

[gentzen]

• Retrocausality/transactional

Because I wanted to better understand a sketch/drawing in chapter 4 of a "strange book" I was reading

(I currently read chapter 4, it doesn't seem to be as badly wrong as chapter 3, but already well on its way deep into esoterics.)

It is not pseudo-science, but it is not science or popular science either. It would say it is scientifically inspired speculation.

I started to dive a bit into the transactional interpretation (TI). I quickly learned enough to understand that sketch and finish chapter 4 (after which I decided to stop reading that book for the moment).

But the TI was still unclear to me, and I also wanted to understand it, because of its greater time-symmetry compared to most other interpretations. I had already learned that there was disagreement between Ruth Kastner and John G. Cramer about "some details" of TI, and that Tim Maudlin had "disproven" Cramer's original version of TI. Kastner's version seems closer to what I am looking for, but Cramer's version seemed less abstract and easier to visualize. I wondered whether Cramer's version could really work, so I read his 1988, 1986, 1983, and 1980 papers. I actually started with his 1986 paper, but it provided insufficient detail in crucial places, and talked about so many vaguely related stuff (not necessarily wrong, but somehow it was "all over the place"). In the end, I was seriously underwhelmed, and I better appreciated why Tim Maudlin decided to "disprove" TI.

And I also learned that I am not alone in being underwhelmed by Cramer's elaborations:
https://www.amazon.co.uk/gp/customer-reviews/R202O26FF2W72V

I've been fascinated by the Transactional Interpretation of QM since reading In Search Of Schrodinger's Cat many years ago - treating quantum processes as bidirectional interactions in time seems to make all that is mysterious in the quantum world comprehensible. [...]

Unfortunately, when the TI is laid out in detail it disappoints. Although Prof. Cramer seems to believe that the TI is nothing but the mathematical formalism of QM converted into words, a number of additional mechanisms are bolted on to explain how a transaction arises in response to offer and confirmation waves (the interpretation of the Schrodinger wave equation in TI). This part of the process seems to be very unclear, with the description being almost anthropomorphic. Apparently the source of an offer wave selects from the time-reversed confirmation waves it receives according to some sort of hierarchy whilst making sure that conservation laws are upheld.

This seems to require a larger set of rules and mechanisms bolted on top of the QM formalism than even Copenhagen or MW require - and if there is a proposed mechanism for how the selection process happens then its description here is so vague as to be incomprehensible.

So it seems that the Transactional Interpretation is not and cannot be the "correct" interpretation of Quantum Mechanics because at the critical moment it waves its hands and mumbles, leaving gaping questions open about what happens and how it happens during a transaction. Maybe Cramer has a vision in his mind, but he has not been able to set it down on paper here.

I started to read Ruth Kastner's stuff more seriously. This made me realize the "conceptual enormity" of the picture TI is forced to paint, if it wants to have any chance to reproduce the predictions of QM. So now I am completely convinced that Cramer's version never had any chance to be correct, and that Tim Maudlin's "disprove" points into the right direction why it had to fail.

 

[physika]

But the TI, because of its greater time-symmetry compared to most other interpretations.

And regarding the similarity with the Two-State Vector Formalism, what is your opinion?

​

 

[gentzen]

And regarding the similarity with the Two-State Vector Formalism, what is your opinion?

I hope that Kastner's version will be similar to it (that's what I meant by "Kastner's version seems closer to what I am looking for"). The Two-State Vector Formalism is fine for weak-measurement, but it is not obvious to me how to model normal "perturbing" measurements. The time-symmetric versions of CH might allow to model them, but probably in an ugly way that reduces the time-symmetry somewhat:

There is a wikipedia article for the two-state vector formalism. It says:

I got the impression that Reznik and Aharonov came up with a completely different approach, namely instead of two independent hermitian positive semidefinite matrices $\rho_i$ and $\rho_f$, the uncertainties in the initial and final state can be correlated:

But they were well aware of time-symmetric versions of CH:

 

[gentzen]

And regarding the similarity with the Two-State Vector Formalism, what is your opinion?

I hope that Kastner's version will be similar to it

and Cramer's version is very different from it:
https://arxiv.org/abs/1503.00039

The assertion that quantum wave functions cannot be considered to exist in normal space and must be viewed as existing only in an abstract higher-dimensional space, of course, creates a severe roadblock for any attempt to visualize quantum processes. (We note that Ruth Kastner’s “Possibilist Transactional Interpretation”[15, 16] adopts this point of view and treats quantum wave functions as being real objects only in an abstract multidimensional Hilbert space, from which transactions emerge in real space. The possibilist approach is not incorrect, but we consider it to be unnecessarily abstract.)
The “standard” Transactional Interpretation, with its insights into the mechanism behind wave function collapse through multi-vertex transaction formation, provides a new view of the situation that make the retreat to Hilbert space unnecessary. The offer wave for each particle can be considered as the wave function of a free particle, initially free of the constraints of conservation laws and indepent of the characteristics of other particles, and can be viewed as existing in normal three dimensional space. The connections between an ensemble of such free particles is only established when the multi-vertex transaction forms.

 

[WernerQH]

I started to dive a bit into the transactional interpretation (TI).

When I first encountered the transactional interpretation (~1986) I found it very attractive. Its main problem, as I see it now, is its ontology. What exactly is a "transaction"? And I think those "offer" and "confirmation" waves can't be real, neither in real (3d) space, nor in configuration space.

But essentially the same time-symmetric idea is already implicit in Schwinger's closed time-path formalism (1961). The "waves" are just the propagators connecting the vertices, and they "propagate" on the forward or backward time branch, respectively. For me they aren't real, but just elements of a mathematical apparatus that allows us to calculate the probabilities of patterns of events ("histories", if you like, but I don't think of them as continuous, but sequences of discrete points in spacetime).

 

[Fra]

There are also Dirac and Klein-Gordon equations for many-particle states. See e.g. my https://arxiv.org/abs/1205.1992 Sec. 8.3.3.

Not sure why i got back to this old thread, but regarding the OT and "relativistic interpretation of QM" I think indeeed the introduction of fermions (which are as we know hardware to understand classical, what "IS" a fermion really?), and it's relations to bosons (and thus the KG -> Dirac) relations is very central to the OT.

Relating to the qbism comment in post 6, one can reflect over werther the classification of boson vs fermion, is in the eye of the beholder? ie. the agent? After all the KG -> Dirac transformation is a sort of cahnge of variables that we can try to "interpret", does this transformation have a physical meaning that we can try to understand - or not?

/Fredrik

 

[PeterDonis]

werther the classification of boson vs fermion, is in the eye of the beholder? ie. the agent?

It isn't. Boson vs. fermion has experimental consequences.

 

[Fra]

It isn't. Boson vs. fermion has experimental consequences.

Yes agreed, and we can leave it at that, I guess we also get no further clues to the interpretational issues of relativity. I was trying to elaborate a bit as i think the KG/Dirac that is the standard example of introducting relativistic QM in a heuristic manner, with a tang that never left...

Relativity is after all about an equivalence class of observational frames; related by transformations, though referring only to spacetime. The problem is that way we understand this equivalence class in classical physics (SR), is problematic in QM. As QM is primarilty constructed in the observer bias, and this is more so emphasises more strongly in the qbist perspective. But the objectivity is restored if the observations in different views are related by transformations.

This is conceptually what i mean in the "eye of the beholder".

But part of the interpretational issues of QM so some at least are related to the unification to relativity. Many of the deep conceptual problems there are IMO clearly rooted in how we understand this "equivalence class" AND still insist of the observer-frame-bias that is built into the QM foundations.

The interesting thing is that many symmetries or maybe better to say dualities seem to come with the same conceptual problem. And always felt they are related... (meaning extendion spacetime transformations, to transformations that mix also internal degrees of freedom, which is a BTSM topic, but still part of interpretational issues imo)

So in a way I think the interpretation of QM as is, and the "interpretation of observer equivalence" and their relations are interwined, and still unresolved.

We can think of them as unrelated and get on with other things, but I feel that is letting go of a clue we need.

/Fredrik

 

[PeterDonis]

The problem is that way we understand this equivalence class in classical physics (SR), is problematic in QM.

I don't think it's problematic in quantum field theory, since QFT is explicitly modeled using spacetime. The question would be which QM interpretations take account of QFT and base their interpretation on it, instead of on non-relativistic QM.

 

[Fra]

I don't think it's problematic in quantum field theory, since QFT is explicitly modeled using spacetime.

To me it's problematic because this "spacetime" implies an external observer. It's not a problem for any particle physics experiment, but it is conceptually a problem for unification questions.

The question would be which QM interpretations take account of QFT and base their interpretation on it, instead of on non-relativistic QM.

I figured, but what i described would reverse of that logic. Ie. the qbist stands imo more naturally suggests that a qm interpretaiton of the observer invariants is the "wrong way" conceptually, the alternative is to take the observer-biased views more seriously, and allow them to interact, and then find the QFT and the effective "equivalence" class as emergent.

This does not change anything regarding experiments, nor claim that any of the effective theories are "wrong" in any way, it's only a different way of thinking. The main differences is in the view of fine tuning, nature of symmetries etc.

/Fredrik

 

[PeterDonis]

this "spacetime" implies an external observer

No, it doesn't. Classical relativity has no problem at all modeling the observer as being in spacetime, not outside it. The simplest such method is simply to model the observer as having a particular worldline in the spacetime.

conceptually, the alternative is to take the observer-biased views more seriously, and allow them to interact

Do you have any references that expound this kind of model?

 

[Fra]

No, it doesn't. Classical relativity has no problem at all modeling the observer as being in spacetime, not outside it. The simplest such method is simply to model the observer as having a particular worldline in the spacetime.

I meant, the whole construction of quantum mechanics, with state preparations and repeated statistics, and tomography IMO requires a "background" where the units of spacetime, including clocks are defined. IF you change this background context, then the whole quantum phenomenology as deformed (this of course is because we have no unification with Gravity and cosmology). I think this is not controversial, if there is a disagreement i supposed it is because I expressed myself wrong.

In classical relativity we don't have the same issue with non-commuting measurements, so it's not a problem in the same way.

Do you have any references that expound this kind of model?

There is to my knowledge not anywhere near something worthy to be called an explicit model to expound. I was just making a plausible conceptual extrapolation of a flavour of subjective qbist interpretation, not an explicit theory. That in the context of what is relevant for "interpretations of relativisti QM", from my perspective.

But lacking something to "expound", the the conceptual overeally model theoretic context of the is ...

The notion if agent/observer-centerd view contrasts to the system dynamics. But they are not in contradiction, they are just two ways of modelling, having pros and cons.
https://en.wikipedia.org/wiki/Agent-based_model

The "interacting agents" is in AI or computer science called "Multi-agent reinforcement learning"
https://en.wikipedia.org/wiki/Multi-agent_reinforcement_learning

The idea is that "self-organisation" and the "emergence" of effective objectivity may follows from this. some interesting modelling along these lines are

Modeling Others using Oneself in Multi-Agent Reinforcement Learning​

"Self Other-Modeling (SOM), in which an agent uses its own policy to predict the other agent's actions and update its belief of their hidden state in an online manner."
-- https://arxiv.org/abs/1802.09640

Applies to the "agents/obsevers" in physics, this essential would suggest that each part of the universe, encodes a "view" or "effective theory" of it's own environment (which is of course fellow agents). Also not that this seems conceptually close to a hologram.

Autonomous Agents Modelling Other Agents: A Comprehensive Survey and Open Problems​

"A core area of research in modern artificial intelligence (AI) is the development of autonomous agents that can interact eectively with other agents. An important aspect of such agents is the ability to reason about the behaviours, goals, and beliefs of the other agents. This reasoning takes place by constructing models of the other agents."
-- https://arxiv.org/abs/1709.08071

One missing big part is the abstraction of how cow would "inanimate matter" in it's fundamental forms, encode/model/execpt things about it's inaminate environment??

We don't know of course but, one can couple the above idea also to ideas similar to this paper

Law without law: from observer states to physics via algorithmic information theory​

"instead of a world or physical laws, it is the local state of the observer alone that determines those probabilities. Surprisingly, despite its solipsistic foundation, I show that the resulting theory recovers many features of our established physical worldview: it predicts that it appears to observers as if there was an external world that evolves according to simple, computable, probabilistic laws."
-- https://arxiv.org/abs/1712.01826

But as is clear this just dresses up and elaborates the possible promises I see in the "qbist" interpretation, which was the point of hte original post I wanted to comment on.

/Fredrik

 

[physika]

The idea is that "self-organisation" and the "emergence" of effective objectivity may follows from this. some interesting modelling along these lines are

I think otherwise.
(the inverse)

And:
"self-organisation" of what ?
what is "What"
Entities ?
Entities of ?

 

[PeterDonis]

how would "inanimate matter" in it's fundamental forms, encode/model/expect things about it's inaminate environment?

Your use of the phrase "inanimate matter" is a circular argument. The whole point is that if "agents" are made of matter like everything else, then at the very least the matter that "agents" are made of is not "inanimate".

 

[Fra]

"self-organisation" of what ?
what is "What"
Entities ?
Entities of ?

Your use of the phrase "inanimate matter" is a circular argument. The whole point is that if "agents" are made of matter like everything else, then at the very least the matter that "agents" are made of is not "inanimate".

It is true that there is an apparent "circularity" here, but it is indeed part of the open problem. Especially when you try to summarize this briefly, as to keep this on topic. There is a chicken and egg situation. What comes first, the observer or the observed etc. Do you explain one in terms of the other or vice versa? Is one view more fundamental or not?

Some short comments to try to explain without diverging..

I referred conceptually to self-organisation of the ambigous subjective views. The idea is the the self-organisation tames or cures the PROBLEM with the ambigous views. The resulting complex group-dynamics will by assumption work in parallell with the evolution among the views (agent population), so that there will be a steady state where the agent-population matches matter phenomenology, and the group-dynamics matches the matter interactions.

Needless to say this is an open problem, but the benefit if this works in the future is that instead of a finetuning of mathematical modells with parameterspaces (at the system dyanmics level) that has beeen made up or heuristically constructed without insigiht, we will have a evolutionary mechanism that from (agent model level) probably from a managable parameters space (with less fine tuning) that can provide explanation (in terms of the mentioned mechanisms) of the effective structures of system dynamics.

The term inanimate could be questioned yes, but what I meant was to distinguish between the persistent idea of many physicists that "theories/expectations/observation" requires some conscious or higher order context. But the challenge is indeed to understand how to explain the emergence of these apparently "animate" or "living" systems, if they are built from "simple" elementary building blocks, that themselves are not usually though of as "animate". But indeed, one could argue that even a single bit, flipping it's state in response to some enviromnet or data stream is "animate"? If so, you are right, all is animate. It's hard to choose the right terms.

/Fredrik

 

[PeterDonis]

There is a chicken and egg situation.

Only if you assume that "observer" and "observed" are fundamentally different kinds of things. Which is a circular argument. Similar remarks apply to terms like "conscious" vs. "unconscious" or "animate" vs. "inanimate".

Also, you are getting very far afield from QM and into philosophy, which is off topic here. This thread is about relativistic interpretations of QM, not about philosophical questions.