Questions re Cramer's Transactional Interpretation?

[DrChinese]

If TI is correct, then all photons must eventually arrive somewhere (since no photon could start on its journey until a CW existed from the destination).

My point exactly, and the question might lead to experimentally testable predictions. If I aim a beam into far dark space, and consider the on-going expansion of the universe, some percentage of those photons would NEVER be able to land anywhere. By the time they get to the position where something might exist, that matter will be long gone and the light will never be able to catch it. Their emission would be suppressed (assuming that photons are mathematical abstractions or excitations of the EM force). You might imagine that a beam aimed in one far off direction could not be as strong as the same beam aimed at the ground, and you would notice that by measuring power in (and/or heat out i.e. whatever it takes to balance total energy).

If photons can exist as free entities, then there would be no "suppression".

Any comments? RUTA, are photons free particles? Or are they only intermediaries?

 

[RUTA]

My point exactly, and the question might lead to experimentally testable predictions. If I aim a beam into far dark space, and consider the on-going expansion of the universe, some percentage of those photons would NEVER be able to land anywhere. By the time they get to the position where something might exist, that matter will be long gone and the light will never be able to catch it. Their emission would be suppressed (assuming that photons are mathematical abstractions or excitations of the EM force). You might imagine that a beam aimed in one far off direction could not be as strong as the same beam aimed at the ground, and you would notice that by measuring power in (and/or heat out i.e. whatever it takes to balance total energy).

If photons can exist as free entities, then there would be no "suppression".

Any comments? RUTA, are photons free particles? Or are they only intermediaries?

I was just looking into this. Here are two very relevant references both of which can be found online in full when you do a Google search:

Davies, P.C.W.: Extension of Wheeler-Feynman quantum theory to the
relativistic domain I. Scattering processes. Journal of Physics A:
General Physics 4, 836-845 (1971)

Davies, P.C.W.: Extension of Wheeler-Feynman quantum theory to the
relativistic domain II. Emission processes. Journal of Physics A:
General Physics 5, 1025-1036 (1972)

In short, you are right about the fact that most photons are not ever absorbed in many cosmology models. Davies mentions Einstein-deSitter explicitly, for example. Apparently, this is what killed the idea of "direct particle interaction."

As for whether photons are "free" or not, the terminology varies (as you will see in the second Davies paper). Feynman said simply that virtual photons are those with internal lines in the Feynman diagrams, i.e., they're absorbed. For real photons, emission and absorption events are independent of one another. If direct particle interaction is correct, then all photons are virtual per Feynman's terminology.

 

[DrChinese]

References available at these links:

Davies, P.C.W.: Extension of Wheeler-Feynman quantum theory to the
relativistic domain I. Scattering processes. Journal of Physics A:
General Physics 4, 836-845 (1971)

http://cosmos.asu.edu/publications/papers/ExtensionOfWheelerFeynmanQuantumTheoryI%206.pdf
Davies, P.C.W.: Extension of Wheeler-Feynman quantum theory to the
relativistic domain II. Emission processes. Journal of Physics A:
General Physics 5, 1025-1036 (1972)

http://cosmos.asu.edu/publications/papers/ExtensionOfWheelerFeynmanQuantumTheory%207.pdf

 

[DrChinese]

From Davies II:

"The question of whether or not the universe as a whole behaves like a light tight box
is debatable, and a question of cosmology. Should this not prove the case, then the work is still of some academic interest since it tells us something of the structure of QED.

"The original motivation for a direct interparticle action theory of electrodynamics
was the elimination of the selfenergy divergences which plague the conventional theory.
It does not seem possible to quantize the divergent free classical theory in a meaningful
way without re-introducing a form of selfaction."

 

[rkastner]

Hi all, here are some recent papers that deal with questions/comments here:

(1) PTI and Relativity: http://philsci-archive.pitt.edu/8952/

Among other things, describes how to understand 'absorption' for those concerned that it's not well-defined

(2) De Broglie waves and spacetime: http://arxiv.org/abs/1107.1678

Also, in response to Dr. Chinese, I would note that the 'field' in a direct action (DA) theory is not quantized in the QFT sense, since the quantization implies independent degrees of freedom of the field which don't apply in the DA case. Thus the TI picture does not require a quantized field. Quantizing the field allows for practical calculations, but the direct action picture can be seen as the underlying ontology if all emission and absorption sites are taken into account, which is not possible in practice. The point is that the TI picture describes an underlying ontology not accessible for pragmatic purposes. In that sense it can be viewed as an explanation of the physics underlying the practical calculations of QFT in the limit in which one could know all the sources/sinks (i.e. from a 'God's eye view').

 

[bohm2]

Hi all, here are some recent papers that deal with questions/comments here:

(1) PTI and Relativity: http://philsci-archive.pitt.edu/8952/

Among other things, describes how to understand 'absorption' for those concerned that it's not well-defined

(2) De Broglie waves and spacetime: http://arxiv.org/abs/1107.1678

Thanks. I really enjoyed your second paper. I posted it in another thread previously. I'm looking forward to reading the first one you provided. Curious, how does this model deal with Maudlin's criticism of retrocausality and also Peter Evan's claim:

that what the transactional interpretation is missing is a causally symmetric account of the transaction mechanism: that is, both initial and final boundary constraints with equal causal significance influencing the dynamics of the system. Such a causally symmetric mechanism would serve to ensure the coherent mutual adjustment of all the relevant free variables.

http://arxiv.org/PS_cache/arxiv/pdf/1011/1011.2287v1.pdf

 

[RUTA]

Hi Ruth, Mark Stuckey here.

I read the first paper and it seems to make sense. However, I've been fooled into thinking I understood PTI before My first question involves your statement:

"A photon does not exist in spacetime unless there is an actualized transaction involving an offer wave and a confirmation wave," p 29

How do you account for the belief in stellar astrophysics and cosmology that the majority of photons emitted by stars will never be absorbed?

 

[rkastner]

Thanks, Bohm2; for my reply to Maudlin-type challenges, see:

http://www.isrn.com/journals/mp/2012/617291/

I'm not sure I understand what Peter is looking for here. The actualization of a particular transaction out of a set of incipient ones is not a mechanistic/deterministic process; it is more akin to spontaneous symmetry breaking. I touch on this here:

http://link.aip.org/link/?APCPCS/1408/7/1
A preprint version can be found here: https://rekastner.wordpress.com/the-broken-symmetry-of-time/

Concerning the question from Ruta about astronomy/cosmology, I would need to know what specific physical statement in the field is being viewed as inconsistent with what I've presented re PTI so far. Emitters like stars can emit all the em offer waves they want, and those are often referred to as 'photons' even if no energy is actually transferred from the emitter to an absorber. This may just be a semantic issue.

 

[RUTA]

Concerning the question from Ruta about astronomy/cosmology, I would need to know what specific physical statement in the field is being viewed as inconsistent with what I've presented re PTI so far. Emitters like stars can emit all the em offer waves they want, and those are often referred to as 'photons' even if no energy is actually transferred from the emitter to an absorber. This may just be a semantic issue.

According to standard astrophysics, stars lose mass as they emit photons which carry away energy. According to standard cosmology, most of those photons are never absorbed. According to direct interaction (with which you seem to agree per the quote in my last post), no energy is lost from the emitter unless there's an absorption. This is one reason why direct interaction was ultimately discarded, i.e., it requires a change in stellar astrophysics or cosmology. I have a colleague who has been working on this problem from the cosmology end, I'm just wondering what your resolution would be.

 

[rkastner]

Thanks, could I see a published reference containing this view/argument?

I would, however, note that the question of the actual universal boundary condition is very much up in the air.
Even if we have an 'open universe,' there is a possible mechanism for an absorber-less transaction via a perfectly reflecting t=0 boundary condition. See, eg, Cramer (1983), Foundations of Physics, Volume 13, Issue 9, pp.887-902

 

[rkastner]

BTW, those interested in continuing to discuss PTI can visit my blog, rekastner.wordpress.com; I check that more frequently because I'm updating it regularly.

 

[RUTA]

Thanks, could I see a published reference containing this view/argument?

I would, however, note that the question of the actual universal boundary condition is very much up in the air.
Even if we have an 'open universe,' there is a possible mechanism for an absorber-less transaction via a perfectly reflecting t=0 boundary condition. See, eg, Cramer (1983), Foundations of Physics, Volume 13, Issue 9, pp.887-902

Of course there is no paper titled, "Why no one uses direct particle interaction anymore," but attached is a paper where Davies points out the problem.

 

[Ken G]

To me it sounds like a relatively straightforward application of entanglement. For example, if you have an electron-positron pair that makes two photons, you can say that it is indeterminate whether the energy is yet in the form of the electron-positron, or in the form of the two photons, until a photon is absorbed. However, it is not necessary to absorb both photons-- the entanglement assures that if you absorb one, you have in effect actualized the other as well. I should think the same would hold with a star losing light-- when the gravity of the star is observed, by virtue of it deflecting some other object for example, then the star's entanglements with all the photons it has produced becomes actualized. None of those photons need to be actually observed to know that they have left the area-- that much is clear from the gravitational effects that are being measured by the environment, and the photons are entangled with those gravitational effects. Note, however, that it is crucial that the gravitational effects appear in the form of macroscopic deflections, so are to be associated with all the decoherences necessary to collapse the entanglement and assert that the photons have indeed been created.

 

[RUTA]

None of those photons need to be actually observed to know that they have left the area-- that much is clear from the gravitational effects that are being measured by the environment, and the photons are entangled with those gravitational effects. Note, however, that it is crucial that the gravitational effects appear in the form of macroscopic deflections, so are to be associated with all the decoherences necessary to collapse the entanglement and assert that the photons have indeed been created.

Exactly, you can observe the loss of mass by the gravitational effects, so you know the star has emitted photons. In current cosmology models, most of the photons emitted by stars will not be absorbed. According to direct particle interaction, photons are only emitted if they will be absorbed. Thus, we have a problem for direct particle interaction.

 

[rkastner]

Davies (2004) discusses the standard puzzle of how an asymmetric arrow of time can arise from time-symmetric laws. I address this in my aforementioned paper, "The Broken Symmetry of Time" (available at rekastner.wordpress.com). Of course you need asymmetric B.C. to obtain time-asymmetric phenomena from an underlying time-symmetric dynamics. As I previously noted here, there is a provision for an absorber-less type of transaction in terms of a t=0 reflecting boundary condition; so even if the universe turns out not to be a 'light-tight box,' that is not necessarily a problem for the direct-action formulation of TI. Finally, the PTI picture is not crucially dependent on details of direct action theories such as that of Davies; these just provide a particularly natural backdrop for the transactional process. For example, Chiatti [(1995). “The path integral and transactional interpretation,” Foundations of Physics 25, 481-90] views the TI picture as expressed by the quantum formalism without regard to any particular pre-existing physical theory.

 

[RUTA]

Davies (2004) discusses the standard puzzle of how an asymmetric arrow of time can arise from time-symmetric laws. I address this in my aforementioned paper, "The Broken Symmetry of Time" (available at rekastner.wordpress.com). Of course you need asymmetric B.C. to obtain time-asymmetric phenomena from an underlying time-symmetric dynamics. As I previously noted here, there is a provision for an absorber-less type of transaction in terms of a t=0 reflecting boundary condition; so even if the universe turns out not to be a 'light-tight box,' that is not necessarily a problem for the direct-action formulation of TI. Finally, the PTI picture is not crucially dependent on details of direct action theories such as that of Davies; these just provide a particularly natural backdrop for the transactional process. For example, Chiatti [(1995). “The path integral and transactional interpretation,” Foundations of Physics 25, 481-90] views the TI picture as expressed by the quantum formalism without regard to any particular pre-existing physical theory.

"The question of whether or not the universe as a whole behaves like a light tight box is debatable, and a question of cosmology. Should this not prove the case, then the work is still of some academic interest since it tells us something of the structure of QED." Davies, J. Phys. A: Gen. Phys., 1971, Vol. 4.

"Thus D and DF give the same results in all nonradiative processes, provided we live in a universe which absorbs completely all positive frequency disturbances on the future light cone. Many cosmological models, for example, the Einstein-de Sitter model, do not satisfy this requirement." Davies, J. Phys. A: Gen. Phys., Vol. 5, July 1972

"Every second the Sun radiates 4 ×10^26 joules, most of which vanishes into the depths of space, never to return, representing a huge increase in entropy. This profligate expenditure is paid for by the nuclear fuel in the solar core that is used up and its free energy is dissipated around the universe. Over billions of years the Sun steadily and irreversibly burns through its finite stock of fuel, and in time it will burn out and die. The same general story applies to stars across the universe." Davies 2004 attached previously

You haven't addressed the problem. You stated that "A photon does not exist in spacetime unless there is an actualized transaction involving an offer wave and a confirmation wave," p 29. Thus, energy transfers don't occur unless there is absorption, just as in direct particle interaction, so you have the same problem they do with stellar astrophysics and cosmology. What is your resolution?

 

[rkastner]

As I've indicated earlier, it's possible for a photon to exist in spacetime via an absorberless transaction (e.g. as suggested in Cramer 1983). In that type of transaction, the role of 'confirmation' is played by the reflected advanced wave from the emitter at the t=0 boundary condition. Perhaps it's not the kind of 'confirmation' you have in mind, but it functions in the same way, to build up the OW to full strength and allow for asymmetric propagation. Davies' comments that you've cited here consider the standard emitter-absorber picture of a direct action theory, and his approach generally includes the usual DA idea that the field does not exist as an independent entity. In contrast, as I've tried to make transparent in my 'PTI and Relativity,' PTI differs from this ontology by taking the field as physically real and thus leaves open the possibility of other ways in which transactions can be realized, such as this t=0 reflecting boundary condition, which are not typically considered in connection with DA theories. Thus, PTI is not just a 'DA theory' in the traditional sense. My p. 29 sentence that you quoted can be understood as encompassing an absorberless, t=0 perfectly reflecting boundary condition resulting in an effective confirmation in the sense I've described above.

 

[rkastner]

Just a note that I've uploaded my "On Delayed Choice and Contingent Absorber Experiments" to the PhilSci archive: http://philsci-archive.pitt.edu/8963/

This paper argues that Maudlin-type experiments present no more of a challenge to TI than delayed choice experiments present for standard qm. Question/comments welcome at my website, rekastner.wordpress.edu.

 

[RUTA]

As I've indicated earlier, it's possible for a photon to exist in spacetime via an absorberless transaction (e.g. as suggested in Cramer 1983). In that type of transaction, the role of 'confirmation' is played by the reflected advanced wave from the emitter at the t=0 boundary condition. Perhaps it's not the kind of 'confirmation' you have in mind, but it functions in the same way, to build up the OW to full strength and allow for asymmetric propagation. Davies' comments that you've cited here consider the standard emitter-absorber picture of a direct action theory, and his approach generally includes the usual DA idea that the field does not exist as an independent entity. In contrast, as I've tried to make transparent in my 'PTI and Relativity,' PTI differs from this ontology by taking the field as physically real and thus leaves open the possibility of other ways in which transactions can be realized, such as this t=0 reflecting boundary condition, which are not typically considered in connection with DA theories. Thus, PTI is not just a 'DA theory' in the traditional sense. My p. 29 sentence that you quoted can be understood as encompassing an absorberless, t=0 perfectly reflecting boundary condition resulting in an effective confirmation in the sense I've described above.

So, there are no advanced waves representing a completed/actual transaction, only advanced waves from sources that will not receive the photon, and these still manage to "build up the OW to full strength" allowing for an ... emission? I wouldn't can't call it a transaction, since the photon will never be received. So, if all possible ... whatevers ... aren't represented by advanced waves, what's the point of advanced waves? Why not simply use the standard retarded wave explanation? We have photon paths in spacetime, presumably all equally 'real', some of which are represented by both retarded and advanced waves while some are only represented by retarded waves. And what happens to your basis for the Born rule when you have actual spacetime paths without the overlap of advanced and retarded waves?

 

[rkastner]

As Cramer discussed in his 1986 and in the 1983 to which I've repeatedly referred you, there can be different types of 'transactions'. The crucial aspect of an actualized transaction in PTI is just the actualization of a quantum of the respective field that can carry away energy from a source. It's your inference, not mine, that this process *requires* that the energy be received somewhere. I've discussed it in terms of energy transfer from a source to an absorber because that is the situation we deal with in all experiments, and what any interpretation must address. You now apparently would like to extend this approach to more speculative questions about the large-scale structure of the universe. If the universe really is not a (mostly) light tight box, and you demand that PTI account for how stars can radiate away energy into infinite future (which again is not established incontrovertible fact), I have already provided a mechanism involving a less typical type of transaction, which Cramer proposed nearly 30 years ago, so clearly TI’s originator has long been aware of this consideration. Whether or not you'd like to call this a ‘transaction’ is a matter of taste (and evidently is not to your taste) but it contains the same physical properties associated with the typical transaction: cancellation of advanced waves for time less than the emission time and reinforcement of retarded waves for times greater than the emission time.

As for the Born Rule, this applies to situations involving the physical possibility of the detection of a quantum. An infinitely propagating quantum cannot possibly be detected, by definition. If what you are arguing is that the object |x><x| does not seem to apply to this atypical kind of transaction, that would be consistent with the idea that its probability of detection must be undefined, since by definition is has no possible detector.

Re your statement begnning with "if all possible ...whatevers...aren't represented by advanced waves'' : I'm not sure what you are trying to say here. Typical incipient transactions are represented by encounters between OW and CW, viz: |x><x|, not just advanced waves. Also recall that any emitter emits both OW and CW (or at least 'emitter advanced waves') and it is cancellation of the emitter's advanced waves together with reinforcement of its OW that makes possible the transport of a real quantum in the form of retarded radiation. So there are still advanced waves involved in the atypical transaction; and it is their overlap with their out-of-phase reflected retarded component that builds up the field to full retarded strength and defines a quantum being emitted from the emitter and continuing on to the infinite future without being absorbed.

There are many reasons why I think the purely retarded picture of radiation is insufficient. Among these is the ad hoc nature of the ‘free field’ needed to account for loss of energy by a radiating source, and the complete lack of a physical basis for the Born Rule and for a solution to the measurement problem. Here’s a place to start for anyone wishing to consider these issues: http://rekastner.wordpress.com/the-broken-symmetry-of-time/ ; particularly sections 3 and 4; and of course this is also discussed in my http://philsci-archive.pitt.edu/8959/ .

 

[RUTA]

... there are still advanced waves involved in the atypical transaction; and it is their overlap with their out-of-phase reflected retarded component that builds up the field to full retarded strength and defines a quantum being emitted from the emitter and continuing on to the infinite future without being absorbed.

This explains my confusion -- I didn't know you could have CWs connecting x to infinity. Thus, there is no problem posed by the fact that the current reigning cosmology model (LambdaCDM) permits emission to infinity. This is very different than direct particle interaction (obviously), and I didn't realize you had made this change.

I don't have any other questions for you now ... maybe I'll generate more for your presentation in Miami next month. Have a safe trip down!

 

[rkastner]

If you look at Cramer 1983, he explains how the 'absorberless' transaction works. It all looks physically consistent to me. The reflected advanced wave from the emitter continues on to t=infinity in an open universe. We do have to keep in mind, however, that the 'current reigning cosmology' is not incontrovertible fact and should not be taken as ruling out any given interpretation even if the latter does not seem obviously harmonious with it. We are continually learning new things in cosmology and who knows how that will ultimately turn out...

 

[RUTA]

We do have to keep in mind, however, that the 'current reigning cosmology' is not incontrovertible fact and should not be taken as ruling out any given interpretation even if the latter does not seem obviously harmonious with it. We are continually learning new things in cosmology and who knows how that will ultimately turn out...

If a strong interpretation of QM is incompatible with the reigning cosmology model, I would say cosmology is probably wrong. That's actually how I expected you to respond

 

[rkastner]

As I explained , however, the interpretation (PTI) is *not * incompatible. But thanks for characterizing it as a strong interpretation.

 

[RUTA]

As I explained , however, the interpretation (PTI) is *not * incompatible.

To my surprise.

But thanks for characterizing it as a strong interpretation.

You're welcome.

 

[HelpNowPlease]

If yes, then why there is an appearance of the wave function collapse?

There is only something to collapse, if it has something to deflate in the first place.

Maybe the real question is, whether the wave function is objective or subjective. In other words, it is merely a field which is there for us to keep track of our calculations? Early quantum field theorists thought exactly that. But of course, we can't truly believe this today. What we might really believe is there is a battle to prove maybe the wave function is physical and tangible, not some ethereal field of probabilities.

 

[HelpNowPlease]

There is already evidence pointing to the physical interpretation of the wave function.

 

[Maui]

The biggest objection to a probability wave being real seems to be that the majority can not believe it(that the world is like that based on their personal preferences, despite all the evidence to the contrary).

 

[rkastner]

There is a recent proof by Pusey et al that the wave function cannot be considered merely as a statistical quantity describing our incomplete knowledge of quantum entities with real (but unknown) properties. See: http://arxiv.org/abs/1111.3328.

There was also a reply on the arxiv pointing out that the Pusey et al proof depends on realism about quantum objects (i.e., that they do have real but unknown properties). I do not recall the author(s) of that paper, but it argues that the proof does not rule out instrumentalist views of the wave function (or quantum state). As is probably evident from my work, I think that the quantum state does indeed refer to a real entity and that's what explains the predictive power of quantum theory. I am almost finished writing a book on my 'possibilist' variation of TI (PTI) and I hope you'll stay tuned for that. These possibilities may seem 'ethereal' compared to concrete events, but they are crucially important for the inception of a concrete event. I invite anyone interested to drop into my blog, rekastner.wordpress.com. Happy New Year, everyone!

 

[bohm2]

There is a recent proof by Pusey et al that the wave function cannot be considered merely as a statistical quantity describing our incomplete knowledge of quantum entities with real (but unknown) properties. See: http://arxiv.org/abs/1111.3328.

There was also a reply on the arxiv pointing out that the Pusey et al proof depends on realism about quantum objects (i.e., that they do have real but unknown properties). I do not recall the author(s) of that paper, but it argues that the proof does not rule out instrumentalist views of the wave function (or quantum state).

I didn't think the PBR theorem (or any theorem) can rule out the instrumentalist view. Leifer argues that such views are next to impossible to rule out:

I would classify the Copenhagen interpretation, as represented by Niels Bohr, under option 2 (e.g. Wavefunctions are epistemic, but there is no deeper underlying reality). One of his famous quotes is:

There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature…[4]​

and “what we can say” certainly seems to imply that we are talking about our knowledge of reality rather than reality itself. Various contemporary neo-Copenhagen approaches also fall under this option, e.g. the Quantum Bayesianism of Carlton Caves, Chris Fuchs and Ruediger Schack; Anton Zeilinger’s idea that quantum physics is only about information; and the view presently advocated by the philosopher Jeff Bub. These views are safe from refutation by the PBR theorem, although one may debate whether they are desirable on other grounds, e.g. the accusation of instrumentalism.

Can the quantum state be interpreted statistically?
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

Not that I buy this author's arguments but maybe you mean this paper?

Pusey, Barrett and Rudolph claim to prove that statistical interpretations of quantum mechanics do not work. In fact, their proof assumes that all statistical interpretations must be based on hidden variable realism. Effectively, the authors demand from the start that reality must be decided by mathematics, and not by measurements. If this unjustified assumption is dropped, the quantum formalism has a natural statistical interpretation that fully explains the paradox presented by the authors.

The quantum state should be interpreted statistically
http://lanl.arxiv.org/PS_cache/arxiv/pdf/1112/1112.2446v1.pdf