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Welcome! Here you will find information about the latest, relativistic version of the transactional interpretation of quantum mechanics, ‘RTI’, blog posts, and an opportunity for informal discussion. The transactional interpretation (TI) is a new way of understanding what’s behind the formalism of  quantum physics.

My new book for the general reader, Understanding Our Unseen Reality: Solving Quantum Riddles, was published in 2015 by Imperial College Press. UOUR.cover

Here is link to my 2012 book, The Transactional Interpretation of Quantum Mechanics: The Reality of Possibility  

Preview material from the above book: chapter 7

I recently joined the Starytime Podcast to discuss TI. That episode is available here:http://starytime.weebly.com/stary-time-podcast/episode-008-dr-ruth-kastner-unseen-realities (interview begins at 15 min)

You can listen to an introductory talk on TI and the Measurement Problem at Exelis, Inc. here: Introduction to PTI Here is the accompanying Powerpoint: The Transactional Interpretation

Some of my papers: The Broken Symmetry of Time

On Delayed Choice and Contingent  Absorber Experiments

PTI and Relativity

Here is part 1 of a podcast/Minilecture entitled “Appearance and Reality 1,” created for an extra-credit conference in an online Science and Religion course. It is an introduction to metaphysical questions relevant to the interface between science and religion. Here is part 2 of this minilecture: Appearance and Reality 2

26 thoughts on “Welcome!

  1. I was so happy to see (on arXiv 4/25/12) that you are still advancing the transactional interpretation and may author a book on it. I got into physics with the goal of understanding the natural world but was thwarted by how QM was taught (I read Bohm before taking my first QM class). I am now a retired engineer and am trying again to make sense of QM (Sakarov toast: “To the success of our hopeless cause!”). Since I read TI back in the 1980’s, I believe that TI must be included in any correct QM interpretation. One problem I would like to see addressed is how TI can work for stationary state atomic bonding (e.g., H2+) where psi*psi enhances effective e density between atoms. I like your “possibilist” clarifications and have been calling them sub-QM simulations of all possibilities (e.g., how does a single photon go through glass? To get an effective index n, it must interact with billions of electrons in the glass– that must be done in pre-sub-background prior to detection. ). That also suggests that each cubic femtometer of space is similar to an awesome computer of some sort. I’m not that worried about collapse/measurement because it could be that Nature really does use an effective random number generator rather than some complex emergence process (I picture the wavefunction carrying a pointer key like say the theta,phi angles on a unit sphere– and a choice may be made by closest match with a similar pointer on an absorber). TI hasn’t been accepted as much as it deserves. Keep up the good work.
    Regards, Dave Peterson (MS’68).

    1. Thanks, Dave! I’ll look into the atomic bonding situation.

      Re index of refraction: technically this involves scattering, so in that sense it’s not the ‘same photon’ propagating through the glass. It’s similar to the scattering described in my arxiv paper, but with a photon OW interacting with Dirac fields in the glass molecules and being changed in the process. But I agree with your point that all of this happens on a sub-empirical level.

      I’m hoping that my book might help to open up the discussion a bit for reconsideration of TI.

      Thanks again,

      1. If I may add a few more comments:
        Since the sub-quantal reality is so different from our classical reality, language and terms are difficult. Bohr discouraged discussion by insisting that sub-QM be described by classical terms (if at all), and having so many different interpretations of QM impacts agreements on terms. The word `real’ is especially dangerous. In TI, the `reality of psi’ is similar to the `sound of one hand clapping.’ The `one hand’ is real, but not much in classical terms. As a weak expression, psi lives in the `square root of reality.’ Psi may be called a superposition and interference of all `possibilist information’, and PTI is a necessary addition to TI. It is conservative and responsible (and I don’t think it should be controversial) but might go much further. We may never know the true nature of the information substrate, and it would be nice to have a name (WEB, spacetime network, Wilczek’s GRID?). For now, possibilist world may have to suffice.
        I am not sure that the term `pre-spacetime’ is appropriate. TI’s pseudo-time may make `sub temporal’ acceptable, but emergent spacetime is more of a quantum gravity (e.g. spin networks) concept rather than a QM concept. I have some trouble buying philosophical arguments for QM emergent spacetime. In-between end points, there may be only fields [e.g., ArXiv 1204.4616] and they are non-local (and non localized), but that doesn’t mean they aren’t in spacetime. A photon may not have `particleness’ until its path endpoints. I think of wavelength and frequency as information codes for endpoint momentum and energy. I don’t know how other quantum information is coded (other dimensions?). Pre-energy, sub-empirical, pre-classical … I think I like `sub-quantal reality’ – the reality that can lead to a `quanta.’
        I like your discussions in [ArXiv:0906.1626]. The difference between time dependent processes and time-independent states could be emphasized. TI explains the Born rule for time dependent processes, but the Born rule operates in time independent states without any collapse or potential measurement.
        I thought there was a problem with Cramer’s theory of neutralization of waves behind the emitter in that absorber theory assumes 4-pi coverage but TI only talked about one or a few possible absorbers (and often about just one dimension). The neutralization depends on every direction of offer wave eventually encountering some responder. Maybe that was implicit.

  2. Agreed: Psi (or more generally the quantum state) does not describe something that exists in classical terms, but as you note, “real” is a dangerous term because it is generally equated with ‘classical’.

    The reason I don’t think Psi exists in spacetime at all is because of multiparticle states: these have too many dimensions to fit into the 3+1 dimenstions of spacetime.

    Chapter 8 of my forthcoming book describes how spacetime can be seen as emergent from a realm of quantum possibilities. In fact, I think you will find much of what you say above addressed in the book (I talk about the history including Bohr’s take on QM).

    Re Cramer’s 1986: yes, it is assumed that the ‘future absorber’ is complete in that presentation. Cramer has an alternative for cancellation of all remnant advanced/retarded waves in case of an incomplete absorber: perfectly reflecting past boundary condition.

  3. Hi Ruth

    I became interested in TIQM last year and wrote Prof Cramer with some comments and questions but never got a reply. (Is he still active research?) I am posting my email here so that maybe you or anyone else who reads it can reply or comment.

    From: Colin Naturman [mailto:naturman@wbs.co.za]
    Sent: 12 September 2011 09:26 PM
    To: ‘cramer@phys.washington.edu’
    Subject: RE: Advanced light waves

    Greetings Prof. Cramer

    I realise that you are probably too busy to reply. I have started working through your papers starting from the 1980 Generalized Absorber theory paper. I see that what I said in my previous email about the emission of the advanced wave backwards in time is indeed understood in the conventional interpretation to be a description of an ordinary wave coming from the past and being absorbed.

    The way I see it WF absorber theory gives equal weight to advanded and retarded solutions but I am not convinced that it has any real “physical content”. If I give $10 to you over an interval starting at t1 and ending at t2, a WF treatment would say that over the interval t1 to t2, I give $5 to you and you give an additional $-5 to me backwards in time and that for t > t2 I am continually trying to you give you $5 while you are continually trying to give me $5 so that we keep calling it quits, and that for t < t1, I am continually trying to give you $-5 backwards in time while you are continually trying to give me $-5 backwards in time so that again we call it quits. All very nice and symmetric in the use of both a 5 and a -5 but ultimately just a case of playing games with numbers and language, because the net observable physical result is that no transfer of money occurs for t t2 and that in between t1 and t2, $10 gets transferred from me to you.

    The way I see it, if something quacks like a duck, we should call it a duck and an advanced wave carrying negative energy backwards in time quacks like an ordinary wave carrying energy forward in time, so lets just call it that. The biggest weakness of the transactional interpretation is the pseudo-time narrative of which talk of waves going backwards in time is part and parcel. I am interested in understanding what the transactional interpretation is actually saying if we drop the talk of backwards propagation in time which despite its obvious appeal is nevertheless dubious on at least linguistic and philosophical levels if not physical as well.

    I have read Ruth Kastner’s Causal Loops paper and agree with her analysis of the probabilities and I would add that even without going into the probabilities, Maudlin’s criticism of the transactional interpretation is invalid anyway because he confuses the pseudo-time narrative with actual time, when it is instead an informal heuristic argument based on the dubious notion of backwards in time propagation.

    For me the gist of the transactional interpretation is that there is more than just the usual wavefunction Psi present, there is also the so called “confirmation wave” which if we drop the backwards time talk, is present together with the “offer wave” from the start and the combination of the two is the actual physical phenomenon. Although you have allowed for the transactional interpretation to be non-deterministic, my suspicion is that the confirmation wave probably does uniquely determine experimental outcome and that without the dubious pseudo-time echoing talk, there is just the one “chosen” confirmation wave that is physical, other “choices” only exist mathematically. The probabilistic nature of QM would then be the result of our inability to know the “confirmation wave” component, only knowing the “offer wave” component – we can work out what the “choices” are, but we cannot know which of these “choices” is the one that is actually physically present until after the measurement. With the removal of the backwards time and pseudo-time talk, escape from Bell’s inequality essentially amounts to a violation of counterfactual definiteness rather than violation of some form of locality or strong causality. (I haven’t thought through all the details but my suspicion is that without backwards time talk, violation of “strong causality” or locality is actually the same thing as a violation of CFD – whether one says that the value is determined by a future or non-local “cause” (non-locality or violation of strong causality) or that a definite value is “undefined” and meaningless in calculations without a “factual measurement” (violation of CFD), probably amounts to a difference of terminology, and perspective regarding what it means for an observable to have a value, rather than an actual physical difference).

    If and when you have the time, feedback on my comments would be most welcome.

    Dr Colin Naturman

    From: Colin Naturman [mailto:naturman@wbs.co.za]
    Sent: 14 August 2011 04:02 PM
    To: ‘cramer@phys.washington.edu’
    Subject: Advanced light waves

    Greetings Prof Cramer,

    Although you wrote your column on Light In Reverse Gear http://www.npl.washington.edu/AV/altvw08.html way back in 1985, I only came across it last night. Although I had been aware of the concept of advanced electromagnetic waves from when I was a highschool kid in the early 80s, I had never given them much thought, immediately dismissing them as an extraneous solution ruled out by causality. I had some renewed interest around the early 90s when your Transactional Interpretation of QM became widely known but here one was focusing on QM wavefunctions and I gave little thought to advanced electromagnetic waves. I had done my undergraduate degree in both Theoretical Physics and Pure Mathematics but went to on to do a PhD in Pure Mathematics and did not pursue further detailed interest QM after that. I subsequently ended up disillusioned with academic life, particularly the poor remuneration and ended up in the world of IT and software engineering. However I am getting to a point in my life where I have started to have more time to return to academic matters and have been encouraged to return to academic research in particular the foundation of QM as 20 years after doing my PhD people have become interested in applying my results (in the theory of Interior/Closure Algebras which are related to Modal Logic) to various subjects including QM. I am currently catching up on research into the foundations of QM and have been reading papers on the Transactional Interpretation, which to me seems the most promising approach currently available – approaches which attempt to derive QM from probability spaces and orthomodular lattices seem to be a dead end and deeply flawed (despite these approaches being the reason for my renewed interest in the subject). But anyway, back to advanced light waves.

    Last night was the first time I had really given any serious thought to advanced light waves and after reading your article and the discussion of why there seem to be no advanced electromagnetic waves, it struck me that possibly the solution is quite mundane and the real reason is that the mathematical formalism is being misunderstood: Could it not be that the advanced wave solutions are really just an alternative description of the normal retarded waves? If an object A emits an advanced wave at time t1 then at t1 its energy increases (i.e. object A releases a negative amount of energy so its energy is greater for times t >t1 than for times t<t1. The advanced wave travels backwards in time until at some time t0 < t1 in the past it encounters an object B that absorbs it. Then B shows a decrease in energy at t0, it absorbs the negative energy and had more energy for times tt0. Now, for me at least, an obvious question is, how is this scenario any different from saying that that object B emitted a lightwave at time t0 (losing energy in the normal way) and that A aborbed the light at time t1 gaining energy in the normal way? To me it seems that a wave going backwards in time carrying negative energy is just an alternative description of a wave going forward in time carrying positive energy. So advanced and retarded waves are actually the same thing described from different perspectives. Or am I missing something? Your comments would be most appreciated.

    Dr Colin Naturman

  4. HI Colin and thanks for your comments/questions. I will get back to you as soon as I catch up on some other obligations. I do want to suggest that you take a look at my new book which I think may address these. Available in the UK, http://www.amazon.co.uk/

    and making its way across the Atlantic on a ship to the US at this very moment.

  5. Colin, I present (in my recent papers and my book) a new development of TI that I call ‘Possibilist TI’, in which OW and CW are not propagating in spacetime. So the processes that Cramer discusses in terms of ‘pseudotime’ are in my picture sub-empirical, sub-spacetime processes. All absorbers do respond to an OW with CW, however only one of those CW responses results in an actualized transaction and it is only the latter that transfers real energy. I view this process as a kind of symmetry breaking. One paper that disusses the process from the relativistic standpoint is here: http://arxiv.org/abs/1204.5227. A more complete discussion is in my book.

  6. Ruth,

    I have almost finished reading your new book and I think it’s amazing. But there was one part that struck me:
    In chapter 8, you write
    “…, since thoughts and other forms of mental activity are not spacetime phenomena”
    “…thought is not contained in spacetime…” .
    and in a footnote
    “That is, a thought or idea is not reducible to electrical impulses”.

    What do you mean by this? Is there any evidence for this? Are thoughts shown not to be reducible to electrical impulses or is there simply not enough data on this? I tried searching for “Quantum physics and neuroscience” and couldn’t find any scientific articles that would suggest that quantum mechanics was established to be neceassary to describe thoughts.

    I also have a question about the transactional interpretation – it appears to me that the emissions and absorbtions of offer/confirmation waves correspond to terms in perturbative approach to QFT. It seems to me that a Feynman diagram can be associated with each transaction, is it so? You discuss virtual particles in your book, but I think these are merely artifacts of the perturbation theory. Can PTI be defined (or is it in fact defined) nonperturbatively?

    Thank you,


    1. Thanks Peter,
      (1) Nobody really knows what thought is. We can find observable correlates of mental activity–i.e. electrical impulses in the brain–but this does not demonstrate that thought is no more than those impulses. If someone claims that thought is reducible to observable electrical impulses, the burden of proof would be on them to demonstrate this. But since thought is a private, inner perceptual experience, there is no way this could be demonstrated empirically (where ’empirically’ means in a way subject to 3rd-party verification).
      That is, supposed I am inwardly thinking about eating an apple. The only thing observable empirically is an electrical current in a certain part of my brain. But there is nothing about that electrical phenomenon that looks ‘apple-like’; nobody can tell what I am inwardly thinking about just by detecting that current. So clearly there is more to thought than what can be detected empirically.
      (2) Concerning the applicability of QM to mental activity: this is something I’m suggesting, based on my proposal that QM deals with sub-empirical processes. As noted above, thought is something that goes beyond the empirical realm because the content of thought is not subject to 3rd-party observation.
      (3) The basic entity that serves as precursor to offers and confirmations is the propagator, i.e. two-point field correlation. These exist in any interacting field theory. So this is not restricted to perturbative field theory. When we sum Feynman diagrams to get an overall amplitude for a scattering process, we are adding up different orders of a perturbative interaction in which no offers/confirmations are produced. If we have the kind of asymmetry leading to generation of offer and confirmations, this process is pre-empted and we get a transaction instead. So the first case corresponds to scattering and the second corresponds to a radiative process. Let me know if you have any more questions and thanks for your interest!

      1. Dr. Kastner,

        thank you for your answers.

        Regarding 1), I understand that thought are not directly observable by third parties, but that surely doesn’t imply that they cannot behave clasically, as a macroscopic object. Isn’t there a case to be made that due to to enormous number of absorbers in the brain, any quantum state will collapse quickly? Do you see a reason why thought should be exempt from that? Is there anything preventing us to believe that thoughts could one day be exactly reproduced from physical measurements? It seem implausible to me from an evolutionary viewpoint thought should not be susceptible to naturalistic explanations and that it should have some “special” status.

        Regarding 2) Am I to understand that any unobservable phenomenon can be described by QM in your opinion?

        Also, I was wondering if you are planning to provide a more precise mathematical framework for the PTI? That would make it possible to study if it doesn’t contain internal inconsistencies or if some terms are not defined too vaguely, etc. I suspect the lack of such a formulation is one obstacle that might prevent most physicists from considering it seriously.
        Thank you

      2. Thanks Peter, there is a rigorous mathematical framework for the direct-action theory upon with PTI is based. This is discussed in my CUP book and in peer-reviewed papers. More are coming, one in particular focused on antiparticles and why we do not need the Feynman propagator to describe these in PTI.

        Re 1: If thought is something not fully captured by empirical (classical, ‘collapsed’) phenomena, then it could be an aspect of sub-empirical quantum reality. I don’t take a hard line on this, I just allow for that possibility.

        Re 2: no, I don’t claim that any unobservable phenomenon is necessarily described by QM. Rather, I think that QM refers to a class of unobservable phenomena.

        Date: Fri, 18 Sep 2015 13:50:09 +0000 To: rekastner@hotmail.com

  7. Hi, I just finished reading your new book [Understanding Our Unseen Reality, 2015] and am giving it good reviews. But, I do have at least two outstanding questions:

    The Wheeler-Feynman or Davies formulations generally depend on eventually complete absorption. Yet most CMB microwave photons (and most other photons too) haven’t yet been absorbed over billions of years. And, with an increasingly accelerating expansion and diluted universe, it is unlikely they will ever be absorbed. Radiation gravitates. But how real can it be if we have highly incomplete absorption?
    A second challenge is that chemical (covalent) bonding depends on an effective enhancement of electron charge density between nuclei deriving from the Born Rule. This occurs in all bindings without observers or absorbers and is an example of squaring without transacting. However, standing waves may possess some intermediate reality. And they can be viewed as continually reinforced standing wave patterns both in forward-in-time waves and also in backwards-in-time waves. For the Born Rule, perhaps this strong reinforcement is key and above the concept of completed transactions.

    1. Thanks David, I’m glad you’ve enjoyed the new book.
      Regarding your questions:
      (1) The ‘light-tight box’ condition yields empirical equivalence of the Davies theory with standard QED. However, there is nothing to stop the basic direct-action theory from working (i.e. accounting for the Coulomb interaction and for radiated photons) in the absence of a complete light-tight box condition. If that condition were lacking (i.e. if we had only a partial absorption condition), it would open the door for some empirical deviation of the direct-action theory from standard QED. Interestingly, there are some empirical findings that stray from standard QED already (this is discussed in http://arxiv.org/abs/1312.4007 ); whether or not this might constitute support for the Davies theory remains to be seen. Also, Cramer (1983) has given an argument for an alternative to the light-tight box condition based on a perfectly reflecting t=0 boundary condition (this is mentioned in the above paper). So it is not strictly required that the universe be a ‘light-tight box’ in order for the W-F and Davies theories to work. That is just the requirement for exact empirical equivalence with the standard theory. Of course if you had no absortion at all, then the direct-action theory would fail. But we clearly have at least partial absorption.
      (2) I can’t claim to be familiar with the molecular bonding situation you describe here, but if the Born Rule is involved, that would seem to imply that there are absorber responses taking place at some level. I’d be happy to look into this further if you could provide one or more references on this issue.
      Again, many thanks for your interest and questions.

      1. Thanks for your response. Born Rule Enhancement of Electron Density between nuclei:
        To keep things useful yet simple, intro chem classes present sharing electrons (as little balls or black dots) between atoms and talk about valence bond models for how many electrons are needed to complete outer shells. Then they might say that the stability of covalent bonds is due to the build-up of electron density between the nuclei (but don’t say how because that would involve quantum mechanics, and they really don’t want to mention the Born Rule too early). Then PChem books talk about bonding in terms of energy optimizing (but it is just hairy math and the underlying physics picture is kept unclear). They calculate the expectation value of energy that puts PE and KE together. But this mean value formula is already derived from the Born probability P as . Alternatively, we can discuss electron density models for how much effective charge we have between nuclei (a mapping). For the simplest hydrogen molecule we read:

        “The actual electron charge density is given by the square of the magnitude of the wavefunction, and it can be seen that the symmetric wavefunction gives a high electron density between the nuclei, leading to a net attractive force between the atoms (a bond).” http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/hmol.html
        For diatomic halogens, the picture is less clear with a dip/waist weaker density between nuclei largely due to having higher atomic radii (and bonding strength is half).
        Initially beginning with Thomas-Fermi model, modern Density Functional Theory (DFT) also looks at psi*psi for electron density. This makes PE understandable but requires finesse for KE.
        I feel that covalent bonding (time independent Schrodinger Eqn) requires broadening of TI to somehow include continual standing wave reinforcements (some intermediate reality). If the Born Rule were suddenly turned off, most matter would explode! (there would be no chemical bonding). But QM in chemistry is difficult, and physical explanations are still contentious (e.g., 2012, http://cdn.intechopen.com/pdfs/28320/InTech-The_role_of_quantum_dynamics_in_covalent_bonding_a_comparison_of_the_thomas_fermi_and_h_ckel_models.pdf).
        (article is a little lengthy) Thanks, Dave.

      2. Thanks for this–actually I don’t think that the talk here about ‘electron density’ means that there is an absorber response in this context. This is a typical way of discussing the most likely position(s) of electrons, but what is going on is physically accounted for at the ‘offer wave’ level. This sort of bonding takes place at the level of the Coulomb potential which exists in the absence of an absorber response. So I don’t see any problem or conflict here with PTI. This system is just a complicated bound state as discussed in my recent book. Let me know if you have any additional questions/concerns and thanks again!

  8. Could you explain what are the main differences between your two books on the PTI subject :
    The Transactional Interpretation of Quantum Mechanics – The Reality of Possibility
    Understanding Our Unseen Reality – Solving Quantum Riddles

    Is the second one more suitable for an introduction to non specialists readers ?
    Does it contain new theoretical developments, revised discussion ?

    I am presently reading reading the article of Wheeler – Feynman of 1945 (W-F) : “Interaction with the Absorber as the Mechanism of Radiation”. I realize that you are on the edge of this way of thinking physics which started with Mach (not cited in W-F paper), Tetrode, Ritz, Lewis, Wheeler, Feynman, Einstein, Cramer … Woodward (and his space thruster revolution). You are in good company !

  9. Prof. Kastner,

    I am writing after reading your book, “The Transactional Interpretation of Quantum Mechanics: The Reality of Possibility”

    I have a remark and a suggestion regarding Time, and a question regarding Photons – all in the PTI context.

    I fully agree with your perspective about Time. Found the following quote from your book as a close expression to my views about Time.

    “time is precisely the domain of change (or at least the construct we use to record our experience of change)” P. 201

    I think changes are crucial for Time’s existence. Time cannot exist without changes. I understood this by making the simple observation that all the time measuring means or devices use some sort of standard changes for their time measurements. Another observation was that all the Time measuring units are based upon certain standard repeating processes or certain intervals between standard repeating events – all of course entailing some sort of change. There’s also other crucial part for Time’s existence (which is also implied in the quote above) and that is any sort of consciousness, but this part is not relevant now.

    Since Time is bonded with changes, after reading your book, I thought maybe this bond can be used to enhance your arguments about the abnormal (unactualized) reality before the transaction takes place vs. the normal (actualized) reality after the transaction occurs. I have no clue if what I am going to suggest is really accomplishable.

    I suggest showing mathematically that the unactualized reality cannot be affected in any way by any sort of change in the actualized reality. To be more precise, showing that once any transaction takes place producing actualized results, any change to the actualized results in the actualized space-time, cannot ever affect all those unactualized possibilities which were relating to the same actualized transaction prior to its actualization. If this could be shown mathematically, it would entail, considering the Time-changes bond, that the unactualized reality is also Time-proof of the actualized reality, meaning it is outside the actualized space-time.

    PTI explains how the fundamental transactions occur between quantas, when they occur. But can the PTI explain how or why transactions never occur among certain types of quantas like the Photons ?? My apology if the answer to this question is already given in book, which means I have missed it. Then indication of the page would be appreciated.

    1. Dear Yubal:
      Regarding your question “But can the PTI explain how or why transactions never occur among certain types of quantas like the Photons ??”– Transactions occur under circumstances that fulfill the conservation laws. This means that an emission of energy (as part of an actualized transaction) is only allowed for a system that can transition to a stable lower energy state, and similary for an absorption. This is why transactions only occur between objects that are bound, like atomic electrons. Another aspect is that the Dirac field (ie spin-half quanta like electrons) is sourceless, so strictly speaking a photon is not a ‘source’ of electrons even though photons couple to electrons. The coupling between photons and charged particles like electrons is not symmetrical. Charged quanta are sources of photons but not vice versa (to first order).

      Concerning your question about the unactualized reality not being affected by actualized reality: actually, I think there is a give and take between the two. Actualized events such as an emission/absorption pair can serve as the source of new possibilities.

  10. I don’t have a clear view of how the idea of Tetrode is incorporated in the Transactional approach of Physics. My understanding is that Tetrode considered that a radiation could not exist if there was not an absorber able to receive it somewhere in a causally connected future.
    If this is true, it should be impossible to send any radiation towards a black hole, as the confirmation wave emitted backward in time by the absorber inside the black hole (after the horizon limit) should not be allowed to escape it (if I am wrong and the backward radiation is allowed to escape, my example is in difficulty…)..

    1. The challenge here is that Tetrode’s theory is fully classical and does not address the quantum level. According to PTI, the future is not causally connected with the past since it is just a set of pre-spacetime possibilities. The causal spacetime connection is only established as a result of an actualized transaction. Now it’s also important to note that black holes are a classical construct, and there is some controversy as to whether they truly exist in a stable form (the QM information loss paradox). Remember that the classical theory applied to atoms leads to rapidly decaying atoms–so classical physics has a limited range of applicability. We still need a fully quantum theory of gravity to decide whether black holes exist in the way the classical theory seems to suggest–i.e. as singularities in spacetime. This may not be the case.

      1. Thank you for pointing the uncertain status of black holes existence.

        I realize that in the analysis of my experience of thought I should have noticed that it takes already an infinite time, as seen from the emiter position, for the radiation to reach the black hole horizon and that this is sufficient to prevent any ‘handshake’ between OW and CW to occur.

      2. Actually, any ‘handshake’ would occur outside spacetime according to PTI. The spacetime interval between emission and absorption is a secondary property that arises out of the actualized transaction–that’s what creates the spacetime interval between emission and absorption. So in principle there could be a transaction, but from a the emitter’s vantage point the time interval would be infinite.

    1. I have a question. How do Fermions fit into the TI model. Fermions propagation have an AOT based on their charge, energy and spin states. Fermions are never emitted or absorbed. I see no way their propagation between two spacetime points can be modeled as a combination of advanced and retarded waves

      1. Great question. You read my mind. I am just working on this issue now. Indeed, fermion transactions do not involve fermion confirmations. While any field theory can be formally recast as a direct action theory (Narlikar and others showed this), in view of energy conservation and spacetime constraints, fermionic transactions always occur by way of the interaction of the charged fermionic field with the em field. I will be posting something on the arxiv about this very soon. I should add that they are thought of as ’emitted’ and ‘absorbed’ eg from a cathode to an anode, but this is propagation from one bound state to another, never free propagation. This is accounted for very nicely in the transactional picture through photon transactions that indirectly actualize the fermion as an absorber/emitter of the photons that allow its (indirect) detection.

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