How light ‘smells’ all its possible paths from source to destination

“Now in the further development of science, we want more than just a formula. First we have an observation, then we have numbers that we measure, then we have a law which summarizes all the numbers. But the real glory of science is that we can find a way of thinking such that the law is evident.” -Richard Feynman

Quantum theory tells us that light is somehow both a wave and a particle. It behaves like a particle pursuing an ordinary ray-like path in some situations; but in others, its wave nature cannot be ignored. In this post, we revisit Feynman’s delightful account of the principle of least action, which can help to explain the propagation of light under all these changing circumstances. He starts by considering the principle of least time (a simplified form of the principle of least action), about which he says:

“The idea of causality, that it goes from one point to another, and another, and so on, is easy to understand. But the principle of least time is a completely different philosophical principle about the way nature works. Instead of saying it is a causal thing, that when we do one thing, something else happens, and so on, it says this: we set up the situation, and light decides which is the shortest time, or the extreme one, and chooses that path. But what does it do, how does it find out? Does it smell the nearby paths, and check them against each other? The answer is, yes, it does, in a way.”

Feynman liked to picture light as always being a particle, and came up with a way to explain its wavelike behavior based on the particle’s ability to explore all possible paths in spacetime. This is what he meant by his metaphor of light ‘smelling’ its way from a source to a final destination. He thought of a particle of light starting out from its source and exploring all the infinite possible routes to get to a final destination, judging the best route by the way the neighboring routes compare with it in terms of the time they would take. If those neighboring routes take a very different time from the route being considered, that route gets rejected; but if the neighboring routes take about the same time, that route is chosen.

Clearly this is a complicated and sophisticated process! If we think of light as a little particle doing this route comparison for every possible route, we might wonder how light ever manages to get anywhere!

Screen Shot 2016-06-19 at 10.39.30 PM

A photon examining and comparing all possible routes with one another.

It turns out that if we just stick to the wave picture, we can see quite readily how the behavior of light emerges naturally. But one might ask, what happened to the particle nature of light? We’ll see that it emerges after the wave has done its exploratory work.

Below is a slightly modified version of Feynman’s picture of a wave of light encountering an opening in a screen (notice that even Feynman, who thought of light as a particle, had to include their wave nature!). Two different possible sizes of the opening are shown; the dashed lines show the initially large opening closing down to just a tiny pinhole. For the wider opening, a lot of the initial wave gets through, and is relatively undisturbed by its passage through the hole, so it continues to propagate in the original direction (shown in blue wavefronts and the blue arrow). Most of the light is received at point A in a straight, ‘ray-like’ path from the source.

Feynman Figure 1

However, for the tiny opening, the wave is greatly disturbed by its passage, and spreads out as it exits from the hole (this is called ‘diffraction’). This situation is shown in red. We see this sort of thing all the time with ordinary waves, such as water waves. For this case, the light has a much greater chance of ending up at B or C, which was very unlikely with the wider slit.

In the Transactional Interpretation (TI), all quantum objects such as photons are fundamentally wavelike. They do all their basic ‘exploring’ as waves , and it’s only in the very final stage that a particle-like behavior emerges. In TI, a photon begins life as an ‘offer wave’ (OW for short) emanating from an emitter. But at subtler levels (the relativistic level), it turns out that an OW is only emitted if it also gets responses — ‘confirmation waves’ from systems (such as atoms) that are eligible to absorb its energy. The interaction between an emitting atom and one or more (usually many) absorbing atoms is a kind of mutual negotiation, and both are necessary to get the process started. Once the process starts, the OW still has to decide which of many responding atoms it will choose for its energy deposit. All of this goes on in the background, beneath or beyond the spacetime theater. It’s akin to actors taking their places before a scene is filmed–only the final filmed scene is the spacetime process. But in this case, many actors are called but in the end only 2 are chosen: the emitter and ‘winning’ absorber. Then the filming proceeds — and that is the actual process that occurs in spacetime. The selection of one absorber and the delivery of a chunk of energy is the point where the discrete, particle-like aspect enters. The delivered chunk of energy is the “particle” or quantum.

All stages except the final choosing of the winning absorber are carried out with the wavelike aspect–this is the De Broglie wave, named after the French physicist Louis de Broglie, who first proposed that not only light, but material particles like electrons have a wavelike aspect as well.

So in the TI picture, we don’t have a photon of light having to examine all possible paths. We just have a wave undergoing natural wavelike interference. It is that interference that becomes part of the negotiation between the emitter and all its potential absorbers. Some potentially absorbing atoms may not respond at all, if the offered wave undergoes completely destructive interference before it reaches them. On the other hand, the wave can constructively interfere and provide a large OW component that elicits a correspondingly large CW response from potential absorbers that it reaches. Feynman’s ‘sum over paths’ boils down to a description of the behavior of the interfering OW. The particle of light–the photon–emerges only at the final stage, when one of the responding absorbers ‘wins’ the contest and absorbs a quantum of electromagnetic energy–a photon.

24 thoughts on “How light ‘smells’ all its possible paths from source to destination

  1. Could it be this way, that a transaction takes place if and only if the interference at the emitter with the CW *and* the interference at the absorber with the OW *both* have a high enough *probability*? That way, there is no ‘transaction’ required, because the waves (OW, CW) can just propagate and interfere with other waves, among which each other. So, on both ends, the *probability* is what determines if an interaction occurs? So, waves flowing from past to future and future to past, that’s all?

    1. Actually, no: each potentially absorbing atom in the detection screen will indeed respond with a confirmation (CW) that matches the amplitude of the OW component that reached it. This sets up the Born Rule, i.e., each absorber’s probability of getting the photon’s energy is given by the square of the OW component that reached it. This is where we ‘throw the quantum dice’ and only one of those responding absorbers ‘wins’ the lottery. The latter is the indeterministic ‘collapse’. This is what allows us to say why and how a ‘measurement’ occurred and we don’t end up with Schrodinger’s Cat being both alive + dead. Collapse occurs at the level of atoms and molecules because they respond with CW in this way. Thanks for your question!

      1. Thanks! I think I was getting at something like this: Suppose we have a set emitters and a set absorbers (like a light and a screen or something); could it be that the occurence of a ‘transaction’ is *determined* by *both* ends, the probabilites at the the emitter and the absorber? Of course we would have multiple transactions due to the scale of the setup, but my point is that the ’cause’ of a transaction lies in a *symmetrical* handshake (interference or resonance). Does that make any sense? :)

  2. Thanks–in principle it is possible to have uncertainty in which emitter emitted the offer wave, and in that case the process would be more symmetrical. I suppose you could think of it in those terms–certainly there can be no CW response corresponding to the case of complete destructive interference.

  3. Hi Ruth. We talked some time ago here.

    I’m reading your post and once again I find that it makes a lot of sense. Furthermore, I found that it provides me with important ideas. Let me elaborate.

    Recently I’ve been working on the details of the ineraction of what I would refer to as a “system of elemental free-will agents”

    This week I was writting down more or less the following core concepts (in way less words and detail to save you from a long read)

    “Free will agent A would, by choice, radiate an information wave with the intent of stablishing communication”
    “Any free will agent B would–not by choice–be become aware of the radiation from A, and would, by choice this time, radiate a response wave”
    “The free will of the agents allow them to choose when and what information to radiate, but not the radiation itself and whatever external mechanism it might be subject to”

    While in my work these refers to a level of reality that is more fundamental, transcendental, and larger than the physical universe with its subatomic particles, I specifically wanted this model to reflect the ways of nature as much as possible. Or, to put it in the proper direction, I wanted the model to be such that the laws of nature, such as quantum mechanics and relativity, can be seen to emerge naturally from it.

    So, agents had to radiate waves, and waves had to be conditioned in the way we are used to. I therefore added that:

    “There is some sort of generalized “transactional distance” between free will agents, not necessairly of a geometric nature, which determines the properties of the reciprocal radiations”

    The idea here was to state that free will agents are indeed free to choose when and what information to radiate, but they were not free to choose what it is that they “recieve” from the radiations from others (and they where not free to avoid recieving it either).

    Then I realized that I still needed something else, so I added:

    “Any free will agent is free to change its “transactional distance” relative to any other agent”

    But, this was still wrong, so in the end I just drop it.

    Two main things were missing: In this simplistic model, communications are not proper transactions in the way I feel they should. Instead, I just have a step 1 in which information flows from A to B, *then* step 2 in which information flows back to B, but I wanted the “communication” to be a “simultaneous” reciprocal exchange (i.e. a transaction), and this model was clearly not doing that. So rewrote it with a really simplistic single postulate stating something like “A and B simulatneously exhange a communication wave”. That felt even worse, so I drop that as well, and called it a day.

    I always preferred to see, for example, photons as a sort of after-fact that exist only *until* both electrons agree to exchange one. This view is IMHO a necessity from the POV of free will, for otherwise, an electron could choose to emit a photon and then it might happen that NO other electron would ever choose to absorve it, in which case we would experience light dying out into nothingness. I always needed to see actual events in the phenomenological reality as co-creations that emerge from a freeley agreed upon transaction between “agents”. But my model was not conveying this at all, since there were no actual transactions but a sort of tennis court.

    But there was more missing…. Following my model, agent A radiates, then any agent B in the exact same “transactional distance” would have an equal chance to respond, so, how does A *directs* the intended transacton to one B in particular? This is also a fundamental pre-requisite of a freewill model.

    Reading you blog post here, I feel I can improve on my ideas by borrowing yours:

    A freewill agent A would emit, by choice, an OW, any other freewill agent B also respond by choice with a CW, and then a certain “transactional mechanism” that is itself external to both A and B would establish which to A and B engage in the co-creation (or communication, or transaction).

    The idea that the waves (external, and out of the control of the free-will agents) would be subject to interference patterns, even if in a more generalized (or higher dimensonal) way that in your TI, adds a certain “mechanisist” ruling into the freewill system, which is almost required. Furthermore, it seems to me that the effect of the interference into the determination of which two agents effectively engage can be use as the basis to work out how a emitter can freely choose a target, considering that the interference patterns are a function of distance but ALSO a function of the properties of the wave itself. Speficically, in the case of the familiar physical universe, frequency and amplitude, but even in a generalized “hiperwave”, there could be other, possible many, attributes yet it would still be possible to work out a form of generalized interference nonetheless.

    As it turns out, in this general reality that I’m trying to model, these free will agents “already” are vibrational in nature, so it makes sense for them to emit and absorve waves, and, on top of that, this reality “already” contains a “fluid” or “ether” which would be responsible for the mechanisms, such as interference, governing said waves (a la De Broglie as you youself mentioned). By “already” I mean that there are postulates or propositions independent of my attempts here that speak of that.

    Best

    1. Thanks Fernando, PTI is harmonious with this idea that “photons [are] a sort of after-fact that exist only *until* both electrons agree to exchange one.” These interactions are always collaborative in that sense!

      1. Indeed that’s what I figured. Something that I think you can might NOT agree with is the idea that even mass carrying particles and not just photons, gluons, gravitons etc… might themselves be transactions and not directly the entities radiating offer and confirmation waves.
        I entertain that idea because these particles show a highly patterned behavior, even within the range of quantum uncertainty, so from the POV of a freewill system it would seem almost required that these are the transactional construct (or co-creation as I call it) of several entities.
        In that sense I’m very much aligned with the ideas of Tom Campbell and his Big TOE, of which I take that you’re familiar with.

  4. While I still need to decode that paper, I incidentally found on it the answer to a question I had this morning…. when I was reading your post here, I wondered why you spoke of absorbing atoms instead of absorbing electrons, and I figured that it might be that electrons had to be a part of an atom for them to emitt and absorb photons. But I couldn’t remember if that was indeed the case (Collegue was 20 year ago!).
    Now I see in your paper that it is indeed the case and “a free charge particle can neither emit or absob a photon” :)

    I might come back with comments or questions once I’ve diggested the paper.

  5. Some (Wild?) Speculations about Physics and PTI
    C. G. Justus

    Background

    Spacetime and 5 Dimensions
    Minkowski and Einstein introduced time as a 4th dimension, with its use in a 4D spacetime metric. But time is distinctly different from the 3 spatial dimensions that we perceive. We can be at two times in the same place, but consider it a paradox to be in two places at the same time. Although we sometimes think of time as a coordinate of “infinite” extent (e.g. “block” time), this is not the way we perceive it. We can perceive the (3D) space around us as being “infinite” in extent. However, we can only experience time as a “now”. We can only imagine our future; and our past we can only remember (another form of imagining). It is therefore quite appropriate that we treat time in the 4D spacetime metric as an imaginary component (i.e. ict).
    Our basic means of “perceiving” anything is via electromagnetic (EM) interactions. Usually our most important means of perception is visual, which involves optical detection of photons. Photons are the “carriers” of EM waves and the mediators of EM interactions. Our sense of touch is a response to EM interactions between the atoms of our bodies and the objects being touched. All of our (many) other “senses”, whatever their origin, can be traced ultimately to EM signals produced by the “firing” of neurons in our brain.
    Space and time are intimately related – The finite speed of light means that we can perceive very distant objects only as they existed at some time in the past. Note that this introduces a one-way (“arrow of time”) relationship. We cannot perceive distant objects as they will exist in the future (or even as they exist “currently”).
    Kaluza and Klein (KK) introduced a 5th dimension for spacetime with their attempt at a “unified field theory” for gravity and electromagnetism. The KK 5D metric has 15 independent components. Ten components are identified with the Einstein 4D spacetime metric, four components with the EM vector potential, and one component with a new scalar field. The 5D Einstein equations yield the 4D Einstein field equations for gravity, the Maxwell equations for the EM field, and an equation for the scalar field. Kaluza also introduced the hypothesis known as the “cylinder condition”, that no component of the 4D metric depends on the fifth dimension. Our lack of perception of the KK 5th dimension, along with the cylinder condition, has led to the idea that the new 5th dimension is only of very small extent, in a process known as “compactification”. However, we may also consider the KK 5th dimension as just another “imaginary” dimension, necessary for describing the physical interactions that take place whenever we perceive something via EM interactions.

    PTI, Quantum entanglement and the “building” of spacetime

    Two major as-yet-unsolved problems in physics are: (1) how to unify gravity (the general theory of relativity) with quantum mechanics, and (2) how to interpret the apparent paradoxes that result from the mathematics of quantum mechanics (e.g. non-local quantum entanglement effects, such as the “EPR paradox”, and the “measurement problem” inherent in the “collapse” of the wave function). Recently Ruth Kastner has proposed an interpretation of quantum mechanics which provides a resolution for the second of these problems. This “Possibilist Transactional Interpretation” of quantum mechanics (PTI), is described in Kastner’s book Understanding Our Unseen Reality: Solving Quantum Riddles (2015), and in several scientific papers, such as (Kastner, 2012)

    http://arxiv.org/ftp/arxiv/papers/1204/1204.5227.pdf

    In PTI, the quantum mechanical wave function is represented with time symmetrical components, called an “offer wave” (OW) and a “confirmation wave” (CW). Emission and absorption of quantum “objects” (such as photons) are described in PTI by OW-CW interactions.
    Furthermore, PTI may offer a way to resolve the problem of unifying gravity with quantum mechanics. Rather than interpreting OW-CW processes as occurring in a pre-existing spacetime manifold, it is possible, using the concepts of causal sets, to consider the OW-CW interactions as “building” spacetime. As Kastner puts it in the paper (Kastner, 2014)

    http://arxiv.org/ftp/arxiv/papers/1411/1411.2072.pdf

    “spacetime is not a substantive manifold that becomes occupied with
    events; rather, spacetime itself exists only in virtue of specific actualized events.”
    Other researchers have also recently proposed mechanisms whereby spacetime can emerge from quantum entanglement processes (explainable by PTI)

    http://phys.org/news/2015-05-spacetime-built-quantum-entanglement.html

    In the classical (i.e. non-quantum-mechanical) descriptions of general relativity and Kaluza Klein theory, space and time are continuous (the “spacetime continuum”). In contrast, the spacetime manifold that emerges from causal set dynamics and PTI is inherently discrete.

    Speculations

    PTI and the Emergence of 5D Spacetime?

    In general relativity, gravity is not considered to be a force exerted between masses. It is instead the interaction between masses due to the curvature of spacetime in the vicinity of the masses (“Matter tells space how to curve. Space tells masses how to move.”– John Archibald Wheeler). In quantum mechanics, interaction between bodies is considered to be mediated by the exchange of quantum “objects” (e.g. EM interactions between charged particles result from the exchange of photons, the quanta of the EM field). Quantum gravitational interactions have usually been assumed, by analogy, to result from the exchange of hypothetical particles dubbed gravitons. Emergence of a discrete spacetime manifold from causal set dynamics and PTI OW-CW interactions offers a way to quantize gravity without resorting to a graviton exchange mechanism. All that is required is that the interactions between masses due to electromagnetic interactions described in PTI by OW-CW processes produce a discrete spacetime manifold that is “curved” in a way that, in the continuum limit, is consistent with general relativity. Since EM interactions would be inherently involved in this process, it is suggested* that the discrete spacetime manifold thus generated should be a 5 dimensional one, consistent, in the continuum limit, with the Kaluza-Klein 5D metric. [*Note added by REK: just for clarity, this is the suggestion of the author of this comment.]

    Gravity as Residual EM PTI Interaction?

    But how can EM interaction between masses, which can be electrically neutral, produce such a 5D metric? Perhaps a clue is provided by a paper by A.K.T. Assis, who describes the classical (non quantum mechanical) EM interaction between two neutral dipoles. Using a generalized Weber’s Law for EM interactions, he shows that a force equivalent to Newton’s law of universal gravitation results as a 4th order “residual” effect of the EM interaction.

    http://www.ifi.unicamp.br/~assis/gravitation-4th-order-p314-331(1995).pdf

    Perhaps a complete PTI/causal set treatment of the EM interactions due to photon exchange between all of the charged components (e.g. protons and electrons) of electrically neutral masses, can similarly yield a suitably “curved” 5D spacetime metric that describes “quantum gravity”.

    Strong and Weak PTI Interactions as Dimensions 6-11?

    Some recent theories, such as string theory or M theory, hypothesize an 11 dimensional spacetime manifold. The following speculations suggest how PTI might provide a means for generating such an 11 D spacetime metric.
    Two other fundamental forces are the strong interaction, which binds quarks into nucleons, and the weak interaction, which is responsible for radioactive decay of subatomic particles. The nuclear force responsible for binding nucleons into atomic nuclei is known to be a residual effect of the strong interaction, in a manner analogous to the proposal above that gravity is a residual effect of EM interactions.
    It is suggested that PTI OW-CW processes and causal set dynamics,
    when applied to strong and weak interactions can generate a spacetime metric of 11 dimensions, in a manner similar to the generation of the KK 5 D metric by PTI treatment of EM interactions, as discussed above. It is further suggested that these two additional physical interactions contributes an additional 3 dimensions each to the 5D KK metric (5 + 3 + 3 = 11). But if PTI treatment of the EM interaction introduces only 1 additional dimension, why do these additional two interactions introduce 3 additional dimensions each? It is speculated that this is due to the differences between the natures of the force-mediating quanta involved in these 3 interactions. The EM interaction involves only one massless quantum, the photon. However the strong interaction is mediated by massless gluons, which come in three “colors” (“red”, “green”, and “blue”), and the weak interaction is mediated by 3 different bosons (W+, W-, and Z) all of which have mass.

    “Plancktron” as Dark Matter?

    An important length scale for a quantum particle of mass m is its Compton wavelength (the wavelength of a photon whose energy is the same as the rest-mass energy of the particle, mc2). This is often expressed as the “reduced” Compton wavelength

    ƛ = ħ / (m c) ,

    which is the standard Compton wavelength divided by 2 π, where ħ is the “reduced” Planck constant.
    In the system of natural units known as Planck units, mass and length scales are given by the Planck mass

    mP = (ħ c / G )1/2 ,

    and the Planck length

    LP = (ħ G / c3 )1/2 ,

    where G is Newton’s Gravitational constant.
    An important parameter for a black hole of mass M is its Schwarzschild radius RS, given by

    RS = 2 G M / c2 .

    RS is the radius of a sphere surrounding the black hole on which the escape velocity is equal to the speed of light. The surface of this sphere of radius RS is known as the event horizon. A lesser-known parameter for a black hole of mass M is its photon sphere radius rp, the radius of a sphere surrounding the black hole where gravity is strong enough that photons (moving at the speed of light) would travel in circular orbits around the black hole. This radius is given by

    rp = 3 RS / 2 .
    Consider now a hypothetical “Plancktron” particle of mass equal to the Planck mass, and size sufficiently small so as to be a black hole. Straightforward manipulation of the equations above shows that the reduced Compton wavelength, Schwarzschild radius, and photon sphere radius of such a particle are given by

    ƛ = LP ,

    RS = 2 LP , and

    rp = 3 LP .

    Thus all these relevant length scales for the Plancktron are of the order of the Planck length LP.
    Current theories of black holes indicate that photon orbits in the photon sphere are not stable in the long term. They also indicate that black holes as small as the hypothetical “Plancktron” would “evaporate” extremely quickly by emission of Hawking radiation. However, it is conceivable that quantum analysis using causal set dynamics and PTI OW-CW processes may yield distinctly different results. Firstly, such analysis might show that the discrete spacetime metric generated by these processes produces no spacetime points inside the particle event horizon. If such is the case, it would be as if there is not enough ”room” inside the Plancktron event horizon for any space to exist there at all. Such a particle of “no spatial extent”, although not strictly a point mass, may have zero or infinitesimal cross section for interaction with photons or other particles. The dynamics of photon sphere orbits around such a “region” of no spatial extent may also be such that these orbits have infinite or extremely long lifetimes. If Plancktrons exist with such characteristics as this, they would make an excellent candidate for a weakly interacting massive particle (WIMP) form of dark matter, whose only interaction with other matter is by gravitational interaction. Such Plancktrons, likely produced during the radiation epoch following the Big Bang, when photon densities were extremely high, could exist to the present era essentially unchanged.
    The Planck mass is about 2 x 10-8 kg, or roughly 1019 times the mass of a hydrogen atom, so the hypothetical Plancktron is indeed a massive particle compared to conventional nucleons. However, even though dark matter accounts for roughly 80% of the mass of all matter in the universe, the number density of dark matter Plancktrons needed to match observations would be only about 1 Plancktron per 1019 normal matter atoms.

    PTI Photon Sphere as Black Hole “Firewall”?

    One of the conundrums of general relativity solutions for black holes is that they yield a singularity at their origin, the center of the black hole. This singularity has a mass density that approaches infinity, albeit within a very tiny volume, such that the total mass remains finite .
    The observable universe contains about 1053 kg of mass. This amount of mass has a Schwarzschild radius of about 16 billion light years. This is surprisingly close to the distance that light can have travelled during the 14 billion year age of the universe. This lends credence to recent solutions using loop quantum gravity that indicate that our universe is a black hole.

    http://phys.org/news/2012-05-black-hole-universe-physicist-solution.html

    But if our universe is a black hole, why do we see no evidence of a singularity anywhere? And indeed, why is the observed density of the universe so very nearly constant everywhere on a large scale?
    Could it be that the photon sphere around any finite size black hole (i.e. ones larger than a Plancktron) acts as a “firewall” to separate the region of spacetime outside the firewall, where gravity behaves according to expectations of general relativity, from the region inside the firewall where the mass density varies more uniformly than general relativity solutions? If so, might such behavior be explained by causal set dynamics and PTI OW-CW processes?

    1. Thanks for this very interesting comment. Actually, even though atoms are electrically neutral overall, they can engage in em interactions through their residual higher-order multipole em fields. This is how one can increase the temperature of a box of gas molecules–they gain kinetic energy through absorbing infrared photons.

  6. Here are some questions from Jeff Dymek sent to me via FB. I’m posting it here and will reply as soon as I get a chance. Jeff asks:

    “The “solidity” of the empirical world results from the reduction of uncertainty about position. This seems similar to the definition of Shannon information if I’m not mistaken ? Is there a connection or relationship between the HUP and information theory?

    I’ve encountered the block universe in books about the philosophy of time. What I’ve never understood is, how can Relativity tell us both that time is relative to motion, and that there is a static block universe. It’s like saying there both is and isn’t motion. Plus, since there is clearly psychological time/change, the mind cannot be identical to a static 4d brain. I’m not a physicalist/materialist, but that clearly implies dualism. Also, how could collapse be indeterminate if the future exists? If I am right, why don’t professional physicists and philosophers notice/ or address these issues?

    I think your model of reality is fascinating, as far as I’m able to understand it. I wonder if you could take me through ( in layman terms) what’s going on when I use my conscious volition to gaze at a distant star ( that might no longer exist) ? Does a confirmation wave associated with my retina “shakehands” with an offer from the distant past? Or does this even matter since both events are in quantum land? I know this is a weird thing to say, but wouldn’t my choosing to look at the star be part of the reason why it shines/emitted an offer in the distant ‘past’ since an absorber is needed (and my retina is one of many to be sure, but I won the competition between them afterall) ? I would actually love that. It reminds me of something Alan Watts once said that “you shine the sun, but you don’t know how you do it.” (Sorry for the woo there.)”

    1. Here are some replies to your 3 questions:
      (1) Re solidity of empirical world: Actually according to PTI, the empirical world results from the emergence of space-time events from the quantum level, by way of actualized transactions. Once a possibility is actualized as a space-time event, it gains a well-defined position, at least in a relational (not absolute) sense. What I mean by that is that there is no spacetime continuum and events are not mathematical points, they always have some finite extension, of the order of the size of an atom, since atoms are the basic emitters and absorbers. So what we call “position” is really the singling out of a particular atom as the absorber participating in an actualized transaction. Since under PTI this reduction of uncertainty corresponds to a real ontological process, it is probably not best characterized in terms of “information” since that generally implies an epistemic account. I suppose it is possible to relate this to information theory, as long as it is understood that the reason information is gained is because a particular event is actualized that did not exist before – not just because somebody gained knowledge that they didn’t have before.

      (2) Re block world: You actually have several related (good) questions here. First of all, in a block world ontology, “motion” can only be perspectival – i.e., as seen from some observer in a particular inertial frame. In order to tell this story, people who subscribe to a block world ontology have to assume as a primitive fact that there are conscious observers “moving through” the block world. They can provide no explanation for this of course, they just have to assume it. So this gets into your concern about dualism: yes, it does appear to me that there is an implicit primitive dualism here. I don’t have any objection to dualism per se, but this seems to me to be a rather naïve, unexamined version of it. The usual stance is to give priority to a block world ontology and not worry much about observers’ minds – that lies outside of physics, and most block world physicists seem to think that as long as they have a space-time picture that doesn’t violate relativity, they’ve explained everything they need to explain. They don’t seem to feel that it’s important to reconcile our experience of passage with what they think is the correct physical model; they just assume that our experience is illusory or doesn’t need to be taken into account. That is, they don’t see the inconsistency between our temporal experience and the block world model as a threat to that model. Of course, I think that is a mistake.

      Regarding the incompatibility of the block world with indeterminism: some researchers do take into account that a block world implies determinism (or at least a set of determinate future events). But others do seem to be confused about the kinds of restrictions that the block world ontology places on notions of dynamic causation. I tried to clarify this in my talk at the recent AAAS conference. The preprint is here: http://arxiv.org/abs/1607.04196

      3. Re our participation in transactions from stars:
      This is a great question. The short answer is “yes” your retina wins many competitions for photons from distant stars! I will deal with this in more detail in my next book!

  7. Perhaps any other blog post is almost as good for this comment, but here it goes.

    You mention in your books Fearful Symmetry by Stewart and Golubitsky. It seems to me as an engineer that another book Fearful Symmetry by Zee is just as much relevant to your approach, for instance when the author writes about the action formulation. It seems (to me as an engineer) that when Wharton (http://arxiv.org/abs/1211.7081v2) writes about the Lagrangian schema, his approach is similar to your and Zee’s. Also, when you write about nonreversibility of time and energy vs. reversibility of space and momentum, it’s almost disturbing to understand how and why other people disagree on something that is just as obvious to me as that the background on this webpage is purple (Or is it violet?).

    1. Thanks–I wasn’t aware of Zee’s book, will check it out. But my approach is quite different from Wharton’s–he has hidden variables in a block world and thinks of it as a dynamical situation. The PTI ontology is a growing universe rather than a block world. For my critique of approaches like Wharton’s, you could take a look at http://arxiv.org/abs/1607.04196

      1. Perhaps the major reason of disagreement is the complexity of the topic. The closest approximation of what I see as either total causal symmetry and/or the block universe would be an epileptic seizure. If we ignore the “detail” that consciousness and life wouldn’t exist in that reality, a (microscopic or macroscopic) subject equally affected by both past and future events would be stuck and paralyzed in doing nothing at all. So perhaps some of those who assume that SOME causes (or hints about “what is about to have happened”) might be reverse push their opinion a little bit too hard since we definitely are much better at figuring out and witnessing past than future events.

      2. You are familiar with Jeknic-Dugic and Dugic. They have a paper http://arxiv.org/abs/1401.2938v8 written with Arsenijevic on local time. It’s difficult for me as an engineer to figure out what reality is made of and to express my opinion, but on some levels I’ve had for years a feeling of some local time that, in a way similar to observers in quantum mechanics (and waves and particles), the arrow of time in thermodynamic and living systems occasionally becomes messed up, as if the arrow of time on the local level is strongly related to entropy on that same local level, but not totally. It’s like Robert Rosen’s work on anticipatory systems where he just occasionally mentions that time is bizarre (his suggestion that biology is more fundamental than physics) – one of reasons why life and consciousness will never (according to Rosen) be properly modeled and predictable. On the other hand, Dugic for instance disagrees with Prigogine’s opinion about indeterminism and irreversibility, but again not totally.

  8. Dear DrKastner,
    I am always delighted to read your texts about PTI.However,there is one point which I can’t understand.How can we speak about an atom which emits an OW,and a CW that travels towards the past, if the whole process takes place outside spacetime,where surely there are not any possible before,after,cause and effect ?
    Thanks
    Lineu

    1. Thanks Lineu. Remember that the OW and CW are possibilities, so any parameter that labels them refers to a possibility. In the case of the time parameter (either positive or negative), it is a placeholder for what *could* happen if the transaction is actualized. If I understand your concern correctly regarding cause and effect, these concepts need not be restricted to spacetime before/after with reference to a time index. There is a process, yes, but we can think of this as analogous to a process of generation of a symmetry group in mathematics, or an iterative process that is self-generating. It’s meaningful to say that a group is generated by a mathematical entity, even though there is no temporal aspect to it. Similarly, an emitter can be understood as generating an OW, and an absorber generating a CW in response. There is perhaps more ‘physicality’ to this than to a mathematical process, but that’s why I propose that this is another quasi-physical category of existence, beyond the concrete spacetime realm.
      Also, in my books I discuss the ‘knitting’ analogy of spacetime. If spacetime is a knitted fabric, there is a process going on behind that — the knitting itself, which occurs outside the ‘spacetime’ of the fabric and generates it.

  9. Perhaps you could enlighten me once more.I would like to ask about the Block View of time.Suppose I ride my bike a long way in a certain direction.Doesn’t relativity imply that I am walking into the past or future,of ,let’s say,a very distant galaxy?Now,let’s imagine that in this far away galaxy some nice alien is talking to his wife,at this same moment.If I have really penetrated his future,ins’t it acurate to say that the words the alien and his wife exchange were already there,meaning that the future is already written,and there is no free will?
    Thanks!
    Lineu

    1. Using the Knitting metaphor of the fabric of spacetime you describe in your book,I just can’t visualize the map of the future without the contents(events)which take place on the territory.If the Knitting of the future is happening at the same time as my present,it seems evident to me that the transactions that define this future have already taken place(block view).
      Lineu

      1. The trick here is that relativity does NOT imply a block world (even though everyone thinks it does). I refute the ‘proofs’ of this in Chapter 8 of my CUP book (2012). Also, Raphael Sorkin has refuted the block world assumption with a counterexample–he and his colleagues work with a growing causal set model of spacetime. You can have a genuine growing universe and not violate relativity if the new events are added to the set in a Poissonian manner, which is exactly the case in PTI. I discovered the latter fact — that transactions occur in a Poissonian manner — before I became aware of Sorkin’s work. See: https://arxiv.org/abs/1411.2072

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