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Why don't virtual particles cause decoherence? 
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#109
Feb2413, 03:55 PM

P: 381




#110
Feb2413, 04:14 PM

P: 161




#111
Feb2413, 04:25 PM

P: 161

Also, consider an excerpt from Freeman Dyson's essay about how seemingly abstract mathematics has an uncanny way of reflecting the real world: " [Mathematicians] always thought of complex numbers as an artificial construction, invented by human mathematicians as a useful and elegant abstraction from real life. It never entered their heads that this artificial number system that they had invented was in fact the ground on which atoms move. They never imagined that nature had got there first.  Birds and Frogs Freeman Dyson, Notices of the American Mathematical Society, February 2009 


#112
Feb2413, 04:46 PM

P: 161

Saying that there are mediated particles in the scattering process is an attempt to interpret scattering classically, but it's wrong because we don't know what's going on during it. It's totally a quantum process and we simply can compute the amplitudes of the transition from the initial state to the final state. That's it.
Similarly in the double slit experiment, we don't know through which slit a particle went. Saying that a particle went through one specific slit is wrong because it didn't. We can only compute amplitudes for the process of interaction of particle with slit. 


#113
Feb2413, 05:27 PM

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P: 5,366

Ruth, I think you completely missed my post #89
http://www.physicsforums.com/showpos...2&postcount=89 


#114
Feb2413, 06:06 PM

P: 161

“[I]maginability must not be made the test for ontology. The realist claim is that the scientist is discovering the structures of the world; it is not required in addition that these structures be imaginable in the categories of the macroworld.” (1984, ref on request) So we are discovering the real structures of the world. Nothing I've said requires that these be classical (i.e., expressible in 'categories of the macroworld'). In fact quite the opposite. 


#115
Feb2413, 06:28 PM

P: 161

Tom, regarding the gauge issue, PTI is based on a direct action theory so see Davies (1971, 1972) for the precise formalism, which uses the Coulomb gauge for QED. If Nature really uses direct action, this fixes the gauge and there is no ambiguity. So the bottom line: it is an empirical matter what the correct gauge is. The feature of theoretical gauge dependence does not necessarily mean that something is 'unphysical'.
The basis of the perturbative expansion approach is the idea of mediated interactions between field currents, with increasingly accurate approximation to reality with the addition of each order. I think of this as a fractal process; keep in mind that fractals are ubiquitous in nature already.[http://www.wired.com/wiredscience/wp...fractal_10.jpg If you don't want to use perturbation theory, then use a different theory of interacting fields. You will still have to deal with field propagation in some way. My model is realist about field propagation, that's all. I didn't say this is a classical thing and I didn't say that fields chug along classical trajectories, which they don't. I did already address your criterion for calling something 'real'. Basically you are equating 'real' with 'empirical,' when you say things like: "therefore it does not represent reality (in the sense we can define it when we want to have agreement with observations)". This is where the McMullin quote is relevant. 


#116
Feb2413, 10:20 PM

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P: 5,366

I think you miss my point.
We know that perturbation theory is illdefined; we know that especially in QCD there is no phenomenon which allowes for purely perturbative formulation; we know that the gauge artifacts are much more severe in nonabelian gauge theories, so a results for QED don't tell us how to treat them. Eq. (2) using the free propagator D(xy) is wrong in QCD! So for everything which follows after eq. (2) extrapolating QED results is simply not applicable. 


#117
Feb2413, 11:39 PM

P: 161

Tom to clarify, my basic ontology does not depend on their being a purely perturbative formulation. In fact in PTI there is *not* a continuum of spacetime points, so lattice gauge theory would be more natural for my ontology and that is already used in QCD. I do hope you will read my book and consider these ideas and not reject them out of hand. Thanks again for your questions and interest!



#118
Feb2513, 12:24 AM

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P: 5,366

Could you provide some hints what PTI has to say about QFT? I agree that it's interesting as an interpretation of QM, but afaik there is no equivalent line of discussion for QFT (do you know Esfeld's book on "philosophy of physics"? it seems to me that there are no reasonable interpretations of QFT on the market)
In addition: you start reasoning based on your paper, based on propagators and perturbative formalism; once confronted with technical arguments regarding an illdefined starting point and regarding missing key issues your response is to read a book. Does this book contain a nonperturbative analysis of nonabelian quantum gauge theory? If no, then why should I read that book? I still think that you don't address the key issues. But w/o a detailed analysis of these issues and w/o the construction of a welldefined formalism it does no makes sense to interpret a formalism. 


#119
Feb2513, 01:17 AM

P: 381

@RKastner
You are not talking clearly. I bet not even you have exactly understood what you mean by what you're saying, "it's that, but not exactly that, and it's like this but not exactly like this..." This is how you talk all this time, i haven't seen a single real argument about the reality of propagators. You say that if propagators didn't exist then interactions wouldn't exist. Now, what kind of argument is that? Do you know how it sounds like? If [itex]e^x[/itex] represents a real quantity, then every term in the perturbative expansions [itex]{e^x} = \sum\limits_n {\frac{{{x^n}}}{{n!}}} [/itex] MUST BE REAL because if they didn't exist (i.e. weren't present in the expansion) then [itex]e^x[/itex] wouldn't be what it is! If we start interpreting mathematics like that, in whatever branch of science, we are screwed. Virtual $dollars$ will start popping in finance. 


#120
Feb2513, 02:03 PM

P: 161

Regarding the previous post expressing dissatisfaction with what I've said here, and as for 'missing key issues in my response'  as I noted earlier, I have very limited time to spend on this forum. I saw an interesting question the beginning of the thread  asking about virtual photons, to which I thought I might contribute, since I have published work on this topic and I think the model I'm working with is an interesting and fruitful one. No, the model has not been extended in detail to QCD. But neither, to my knowledge, have the following competing interpretations of QM: (1) many world theories (2) adhoc spontaneous collapse theories (3) The Bohmian theory (4) decoherencebased approaches (which, as I've noted, utterly fail to really solve the measurement problem despite their claims), or any other 'mainstream' interpretation of QM of which I'm aware. So why use that as a criticism of PTI? If you yourselves began to explore the PTI model, you might break some new ground and find that it indeed does shed light on some of the issues that you've demanded that I explain here in detail, such as nonAbelian gauge theories. There is a seed here that could be planted and yield fruit, so let's not reject it out of hand. Regarding the impatience expressed by someone here with my asking that you read my papers and my book before making demands for detailed explanations on PF: again, my time to spend here is limited. I saw a question about virtual particles in the context of decoherence, and provided a suggestion that the PTI model has something useful to say about it  especially since decoherence arguments are so inadequate to understanding collapse and determinate results in QM. I've already put quite a bit of time and effort into these publications, and I don't quite see how it's a reasonable request for me to rewrite them all here. It's already out there for you to read. If you read it and you still have questions, I'm happy to engage those. But again, I don't think you'll find detailed interpretive treatments of nonAbelian gauge theories in competing interpretive models of QM. Everettian theories are still struggling to explain the Born Rule in their model. So go ahead and explore the PTI model wrt QCD  I look forward to reading your own work on this. As for the question about the propagator, as I've said repeatedly, quantities such as VEV values of fields  more generally, Wightmann correlation functions  have a welldefined interpretation in PTI as possible offer waves  that is, entities that have a lessthanunity amplitude for becoming offer waves X>  i.e. what you take as welldefined 'quantum systems'. The specific amplitude is given by the relevant coupling constant. I have not 'shifted' my position on this as someone implied above, I've taken note where someone is reading meaning into 'virtual particle' that I did intend. No, of course a 'virtual particle' is not a corpuscle on a worldline so if someone defines a virtual particle that way, that's not, and has never been, what I'm talking about. Re what PTI has to say about QFT, a detailed QFT discussion applying to the PTI model, although he doesn't himself apply it to the transactional picture, is in Davies' papers: Davies, P. C. W. (1970). “A quantum theory of WheelerFeynman Electrodynamics,” Proc. Cam. Phil. Soc. 68, 751. ___________(1971).”Extension of WheelerFeynman Quantum Theory to the Relativistic Domain I. Scattering Processes,” J. Phys. A: Gen. Phys. 6, 836. ____________(1972).”Extension of WheelerFeynman Quantum Theory to the Relativistic Domain II. Emission Processes,” J. Phys. A: Gen. Phys. 5, 10251036. And I address this in some detail in my http://arxiv.org/abs/1204.5227 (FoP) If you read my book, you'll see that PTI does not involve a spacetime continuum, so that's why there is a natural end to the perturbation expansion (if that computational approach is used) and why lattice gauge theory is probably a more accurate underlying framework. In either case, propagators are an essential component of the process and they have a clear ontological meaning in PTI as nascent offer waves (or if you will, 'failed' or 'aborted' offer waves), with the coupling amplitudes quantitatively characterizing their 'nascence' or degree of presence. Yes, these may be unfamiliar concepts, but that doesn't mean they are illdefined. Remember we are dealing with quantum entities, not the classical world, and remember Ernan McMullin's comment. So again, I very much appreciate your interest, and I hope you will continue to explore the TI/PTI picture. Remember that everything about PTI with which you have expressed dissatisfaction or reservations (i.e., certain details not fully explained on this forum, no obvious resolution to the challenge of QCD, etc,  applies even more so to competing QM interpretations. At least TI/PTI can readily explain the Born Rule and the nature of collapse! So put the model to work yourselves, and see what you might do with it, rather than assuming a priori that it will fail. I am available for discussion by way of my website: transactionalinterpretation.org With warm regards, RK 


#121
Feb2513, 03:23 PM

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P: 5,366

Ruth,
I definitly do NEITHER critizise TI/PTI NOR your book which I haven't studied. What I am critizising is that you comment here on a discussion regarding 'existence of virtual particles' w/o addressing the key issues we identified. In case you have a solution, please elaborate (here). 


#122
Feb2513, 04:52 PM

P: 161

Tom not sure I understand your concern. Please specify exactly what problem you see as not solved.



#123
Feb2513, 05:13 PM

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P: 5,366

Ruth, no single problem regarding nonabelian gauge theories and 'virtual particles' has been addressed.
#16, #32, especially #35, your statements But we go around in circles. Asked what I miss (e.g. a single statement on nonabelian gauge theories) you respond either with papers on QED or with your book. 


#124
Feb2513, 05:28 PM

P: 381




#125
Feb2513, 10:43 PM

P: 161

Tom,
If you'd like me to address a specific formulation of QFT not involving propagators, please provide a reference. I've already noted that there is no specific prima facie reason why PTI can't be extended to nonAbelian gauge theories, and invited you to work on that front; and that competing QM interpretations certainly don't provide any detailed account of nonAbelian gauge theories either (because they are too busy trying to explain what is already easily explained in TI/PTI). So let's have a level playing field. Thanks again for your interest, RK 


#126
Feb2713, 12:44 AM

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P: 5,366

Ruth,
I'll check TI/PTI in more detail as soon as I have time. But let's come back to the original question, why virtual particles do not cause decoherence (I do not want to go through all the discussion regarding virtual particles, I simply refer to a perfect summary written by Arnold Neumaier) http://www.mat.univie.ac.at/~neum/ph.../unstable.html My first answer why virtual particles are irrelevant for decoherence was 


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