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Everything posted by bangstrom

  1. I claimed that light emitted from a point and arriving at a point does not necessarily imply that light is a particle at that point because light as a wave can do the same. I answered your question before, Remember my repeated comments about transverse waves not spreading out and light no longer existing at its arrival so its point of arrival doesn’t imply that it ever was a particle? I have also answered similar questions but I don’t recall if they were from you or others and I responded by discussing the Afshar experiments, Poincaré's dot, the W-F absorber, and how light from one atom is only absorbed by a single atom. None of these demonstrate the particle nature of light. Poincaré's dot is worth expanding upon since it speaks directly to your question. Poincaré claimed that a spherical object placed directly in a narrow beam of light should completely block the passage of light, if light is a particle, but if the object is only slightly larger than the beam, light should be able to pass around the obstruction as a wave. Afshar and Flores performed similar experiments with a wire grid. Arago performed Poincaré's experiment using a metal bead on a string and he found that light went around the bead as a wave and landed as a bright dot exactly in the middle of the object’s shadow. So light as a wave can land as a point even if it has to curve around an obstruction. That is an example of light as a wave being emitted from a point and landing at a point. Light responds to its environment beyond what one could expect of light as a particle. Diffraction is one example. If light passes through a single slit it produces a diffraction pattern, If it passes through a double slit it produces an interference pattern, and if it passes through a triple slit, it produces an even more elaborate pattern. How does a photon passing through only one of a triple slit “know” how many slits are to its left or right and act accordingly? If a photon of light reflects from the surface of a frosted glass plate, it reflects a random angles. But if it reflects from a polished surface, it reflects at its angle of incidence. How can a single particle “know” if the area around it is rough or polished? Light responds to the wave like nature of its surroundings, and if those conditions favor arrival at a single point, it will arrive at a single point. That may be particle like behavior but it does not rule out the total wave like nature of light.
  2. The results of the experiment are the same with either view. Only the interpretation of the results is different.
  3. This is looking at the same problem from more than a single point of view. The alternative starts with the conclusion that photons exist and they are particle like. The article explains the results but the part I saw didn't explain the method. The conventional explanation involves the creation of virtual electron-positron particle pairs as I explained and these particles are the source the observed scatter. I explained how it works without the assumption that photons are involved. This is from wiki with the assumption that photons are the actors but whether or not photons are involved, the gamma gamma's observed can be traced directly back to a multi-particle origin. Photon to electron and positron. For photons with high photon energy (MeV scale and higher), pair production is the dominant mode of photon interaction with matter. These interactions were first observed in Patrick Blackett's counter-controlled cloud chamber, leading to the 1948 Nobel Prize in Physics.
  4. Just as means an instant exchange of quantum information and instant is not a speed. This is consistent with SR except for Einstein's 2nd postulate about the speed of light. The value of c in not a speed but a dimensional constant as it appears in Maxwell's equations where c=1/√μo ϵo. The permeability and permittivity of the vacuum limits our ability to observe events at a distance instantly. The NOW here is not the same as the NOW somewhere else. Our observation of distant events is always limited by separation of distance AND time at the constant ratio of one second for every 300,000 km of distance. This observation applies to all observers independent of their individual velocities because it is a constant ratio and not a speed. It is impossible to travel faster than c because c is a ratio and not a speed. Just as you can never travel faster than 1.6 kilometers per mile. Can you give a brief explanation of how the experiment works with particles rather than waves for comparison?
  5. Thank for your lengthy response. I think I see the problem now and it applies broadly to this entire discussion- others included. As for your specific question, I have been answering it repeatedly but my answer was not what you expected so you didn't recognize it as an answer. You have just rephrased your question in words we both can understand, "Schrodinger asked it way back about his cat." That's the question exactly. My answer has been that an excited electron in one atom at the signal drops to a lower orbital as an electron in an atom at the receiver end rises to a higher orbital. It is a non-local exchange of energy among entangled particles. There is no time for an atom to absorb a quantum of energy from the outside because the absorption is entirely internal. It is unsettling to think that an atom at the receiver end has just as much influence over an emission of EM energy as an atom at the signal end but that has been an important part of modern theories of light since Wheeler and Feynman described light as a two-way wave-like connection between signal and receiver with waves going both forward and backward in time.
  6. I use the particle model often, too often- perhaps, because it is largely the only way to explain light as it is generally understood and thinking of light or even a wave traveling through space becomes a habit. Photon theory is what I consider the "old theory" that overtook everything else in the 1920's. The Wheeler-Fynman Absorber theory had one foot in a modern way of thinking about light but the other foot in particle theory and the problem with particle physics is that anything can be explained by the invention of a new particle. Feynman had an infinite number of particles taking every possible path at all possible speeds including speeds in reverse and the theory was too absurd to survive but the W-F Absorber had one advantage over its predecessors in that it always worked. Others, most prominently, John Cramer took the good parts of Absorber theory and got rid of the bad. Cramer defined the photon a a single quantum of energy rather than a space traveling particle and he had a theory that worked. I find that photon theory fails when to comes to explaining modern experiments in QM such as the double-slit quantum- eraser experiment or quantum teleportation. One experiment I find telling is an experiment where two entangled particles continue to communicate non-locally even though one of the particles has been annihilated. This is either some form of quantum necromancy or the entanglement is more likely to reside in the electrons rather than the photon middle man.
  7. It doesn't rule out the possibility. I am not familiar with vapor cells, but if light can pass through a material, its destination lies beyond that point. In QM anything that can happen eventually will happen even at lower levels than expected. But is a photon-photon the source of the scatter? More in my next post. N. Pope is the only person I can recall who cited a specific series of experiments over time to detect photon-to-photon interactions but that is ancient history by now. I did a quick Google and came up with this from 2000 but the article is behind a pay wall. Abstract: "We have searched for stimulated photon scattering in vacuum at a center of mass photon energy of 0.8 eV. The QED contribution to this process is equivalent to four wave mixing in vacuum. No evidence for scattering was observed." Anyone can Google for examples but I think the consensus now is that the problem is not with photon populations but energy levels and lasers can’t deliver the required energy. They say we just need more power. I see no reason to question the CERN data, but mention “photons” and I am inclined to question the interpretation. If light is always a wave and never a particle and photon particles don’t exist, then there should be a wave explanation for the same experiment. I predict the experiment demonstrates the occurrence of a four particle annihilation as the source of the gamma-gamma emission. Not a direct photon photon collision. Here are the preliminaries. From a wave point of view, matter can only exchange energy with other bits of matter. The exchanges can take place locally by direct interaction or they can take place non-locally by means of entanglement. Entanglement involves a wave-like connection between particles prior to the the exchange of a quantum of energy. EM emissions, in this view, involve entanglement between a particle at the source and a particle at the sink. Contrary to photon theory, energy can not exist separate from matter so energy can only be found in places where matter exists. Electrons are the usual stepping stones for a EM signal and the signal goes from en electron at point A to an electron at point B without passing through the the space between. The apparent motion through space is the result of an excited electron in one atom dropping to a lower orbital just as an electron on the receiving end rises to a higher orbital. Energy vanishes from the electron in one atom and appears at another. The only motions are within the two atoms themselves. Those are the basics. For a practical example, if an atom suddenly acquires a burst of energy as if out of nowhere, that energy must have come from most-likely an electron somewhere else. We can draw a wavy line to where we think that atom might be and that line should terminate at an electron source. Back to the experiment. I don’t know anything about the experimental setup at CERN but I can venture a genaric guess as to how it might work. They likely have a detector that suddenly registers a high energy hit. Next you can draw a wavy line back to what you think is the source. The most likely source is at the center of a vacuum where two high energy beams cross and there should be an electron at that point. I don’t know how the electron got there but it is likely a virtual electron-positron pair that suddenly popped out of the vacuum. Virtual particles normally pop in and out of existence without effect, but if they appear in an a high energy environment they could gain enough energy to create a second electron- positron pair. Two electrons and two positrons are an explosive mix and that is the source the gamma-gamma at the detector. No less than the annihilation of the four particles is likely to produce a gamma-gamma emission since the production from one pair needs another pair to act against so the setup is likely to have two detectors at opposite ends of the anticipated event. The experiment demonstrates the presence of four particles in a high energy environment rather than a simple photon scatter. In order to demonstrate the presence of a photon it would be necessary to find a photon schlepping a bundle of energy at any of the empty spaces between two electrons. I will leave it to you or anyone else to give us the correct explanation with photons.
  8. The question you asked me on Nov 9 was, “Re phrasing for absorbtion, Are you telling me you that the electron can 'jump' before absorbtion takes place ? Surely the fundamental question is Which must happen first, absorption, or the electron transition ? “ The question strikes me as asking, Which came first, the shell or the nut? For one thing, you can’t tell precisely when the transition took place because of the impossibility of observing the event and the terms absorption and transition are essentially synonymous. My answer was that I can’t possibly see how anyone can time the events. I could have guessed and said absorption comes first. I suspect that is the answer you were looking for but that is not an answer I can support since I see the timing as unknowable. I have no idea where you are going with your “spectral lines” example so I expect you to explain whatever you are trying to explain. The problem can be viewed theoretically as a problem of math and this has been done by Carver Mead. Carver Mead is a former colleague of Richard Feynman and well known for his innovative work with transistors and IC’s so I suspect he knows what he is talking about. Mead's calculations are time-symmetric with waves going simultaneously forward and backward in time so the concepts of first and last are meaningless. The calculations can be found in the book “Collective Electrodynamics” by Carver Mead in Part 5 “Electromagnetic Interaction of Atoms.” The time of duration in his equations is represented by the letter alpha. I don’t understand Mead’s calculations well enough to give a reliable explanation but it is obvious from his descriptions that he has moved on from photon theory. This is not quite what I am saying. I am saying that two separate particles with different quantum states can share a common existence as if they were side-by-side even though they may be light centuries apart. More specifically, an electron in one part of the universe can share energy with an electron in a another part of the universe by means of entanglement so long as they reside on the same light cone. Why can’t an electron in an excited state couple with an electron in a ground state and the energy be free to oscillate directly between the two? When the oscillation stops, the greater energy level will be randomly found either one or the other of the two electrons. If the energy lands in the formerly ground state electron...we have a transition. With entangled electrons, there is no need for the transition to be local. The entangled electrons could be in atoms galaxies apart. From the perspective paired atoms, an electron in one atom drops to a lower orbital as an electron in the other atom simultaneously rises to a higher orbital. Energy is conserved and there is no separation of energy from matter. The “movement” of energy from one point to another in this view is cinematic like the lights on a moving sign board rather than moving through space. There is no need for the energy in one entangled electron to physically move through space to its partner electron in a ground state. The only motion takes place within the atoms themselves as an energized electron drops to a lower orbital in one atom as its ground state partner rises to a higher orbital in another atom. It is my understanding that this is currently the best model for EM transmission and there are detailed explanations for how it works. The most elaborate model is John Cramer’s Transactional Interpretation TIQM. This is Carver Mead’s working model. A non-local exchange of energy among charged particles not new idea. It can be found in the old Wheeler-Feynman Absorber Theory and in an article published in the Zeitschrift fur Physics by Hugo Tetrode in 1922. “Suppose two atoms in different states of excitation are located near each other, normally it is to be expected that they would have little influence on each other; however, under special conditions with respect to positions and velocities, possibly also in the vicinity of a third atom, it might be that strong interactions occur. Such a situation could well lead to an energy transfer between atoms such that their excited states are exchanged.” Hugo Tetrode- Translation by A. F. Kracklauer. Tetrode explained elsewhere in the article that the two atoms “under special conditions” can be solar systems apart so distance is no consideration. Tetrode also describes their common connection as a Schroedinger wave. His “special conditions” appear to be what we now call ‘entanglement.’
  9. A study was done in the SW USA on blue tail lizards whose only reproduction is by parthenogenesis since there are no males. The lizards are numerous and surprisingly genetically diverse. Somehow, they also overcame the diversity problem. I once worked in a laboratory that only ordered female rabbits from a supplier and it was not unusual to find a pregnant rabbit among the orders. I often wondered if parthenogenesis is possible among rabbits. And how about humans? There is no lack of claimants for a study.
  10. One good bit of evidence “a black swan” is all it takes to falsify a theory. The two experiments fail to give convincing evidence that light is a particle. The photoelectric effect is designed to detect light energy as quanta so it detects light as quanta. It does not necessarily follow that light quanta are necessarily particles or rule out the possibility that light is a wave or even that it occasionally becomes a particle. I have a digital voltmeter that measures DC voltages in millivolt increments. That does not mean that DC voltages are quantized as millivolt particles. Light energy may arrive as quanta and it may be quantized but that does not mean that light is also a little space traveling particle instantly picking up energy here and delivering it to an atom there all at a constant speed relative to a vacuum and at the same speed relative all inertial observers independent of their individual velocities. That sounds like a fairy tale. Light is only emitted in quanta to atoms that can absorb it in the same quanta and it requires two-way, wavelike connection between the signal source and the receiver before the energy transfer is possible. This is the “transaction” part of John Cramer’s Transactional Interpretation of QM. "According to the assumption to be contemplated here, when a light ray is spreading from a point, the energy is not distributed continuously over ever-increasing spaces, but consists of a finite number of energy quanta that are localized in points in space, move without dividing, and can be absorbed or generated only as a whole." Einstein 1905 Naturally, that’s what light is. How do you know it misses? “It is generally assumed that a radiating body emits light in every direction, quite regardless of whether there are near or distant objects which may ultimately absorb that light; in other words it radiates “into space.” ... I am going to make the contrary assumption that an atom never emits light except to another atom.” Gilbert Lewis 1926 I am not aware that photon-photon interactions occur at any energy level and, obviously, not all interactions involve particles. But two photons colliding in space and scattering would reflect particle behavior. Many have claimed that photon particles should collide and scatter when laser beams cross and the experiment has been repeated many times with negative results. The explanation was always that the particle populations were too low. The calculated photon populations are now within the achievable range but no one has yet observed a photon scatter. Afshar’s observation was that particle behavior was never observed in their experiments. I said light energy occurs as quanta but those quanta are not particles in the sense that they are tiny ballistic particles traveling through space. This is a red herring. That’s not being claimed here. It may not be claimed here but that doesn’t make it wrong. It is claimed elsewhere. “Initiating a (light energy) transition requires that signals propagate forward and backward in time, what Einstein called “ the character of reversibility.” Carver Mead 2000 Feynman and Wheeler came to the same conclusion when formulating their Absorber theory. Unfortunately, I find it difficult to to explain light without the common practice of calling a single quantum of light energy a “photon.” We will never get the photon out of our language because it is so useful for explanations but I draw the line at calling a photon a particle. I define the photon to be a single quantum of energy in a EM exchange but not as a little bullet like particle traveling through space. I find understanding light to be more comprehensible and rational without considering light to be a particle and we don’t need no “f” in fotons. Mainstream science moves on. As with most things, progress occurs at the frontier. Einstein later became agnostic about his photon particle theory. "All these fifty years of conscious brooding have brought me no nearer to the answer to the question "What are light quanta?" Nowadays every Tom, Dick, and Harry thinks he knows it, but he is mistaken." Einstein in a letter to M. Besso, 1951
  11. My "I don't see how" was a reply to a suggestion from "studiot." I see no need for rigor.
  12. I am not ignoring previous comments and I acknowledge that energy occurs as quanta and it is absorbed in discrete points but I find this feeble evidence to say that light is ever a particle. If photons exist as particles, there must be some evidence for their presence besides the two examples mentioned. Light is quantized because it is emitted and absorbed in quanta determined by the energy levels of the electrons within atoms. Light arrives at a single atom because light is a transverse wave and transverse waves don’t split, spread, or lose energy as you suggest. Separate transverse waves or scalar waves may diverge with distance but individual transverse waves remain intact. Localized energy is not a property unique to particles. I also find it convincing that a two-way wavelike connection is established between an atom at the source and an atom at the sink before a quantum of light energy can be transferred from one to the other so there is no such thing as a miss or a scatter. If powerful laser beams cross, there is no photon scatter from collisions as would be expected if photons were particles. Even simple things like the Dirac three polarizer experiment are best explained by considering light to be a wave rather than a particle and there are recent quantum experiments that can’t be explained with light as a particle. The Afshar experiment was an attempt to identify photons as particles and it failed to do so. The experiment was thoroughly dammed in peer review as error prone but Flores repeated the experiment with all the sources of error corrected and got exactly the same result- waves but no particles. Light appears to act if it is prescient of its destination and Hugo Tetrode explained in 1922 how charged particles must establish a two-wave wavelike connection before they can exchange a quantum of light energy. This is not consistent with light as a random emission that wanders until it hits a target. Wheeler and Feynman also came to the same conclusion about a two way connection with their overly complicated Absorber theory and the W-F theory evolved into John Cramer and Ruth Kastner’s present day Transactional Interpretation of Quantum Mechanics and N.”Viv” Pope’s and Anthony Osborne’s Angular Momentum Synthesis. The latter pair were adamant about dropping the word “photon” from their writings so as not to confuse anyone with old images of the photon as a space traveling particle. I see no reason or occasion to consider light as a particle and it appears to be an obstruction to understanding how light works. This two-way connection is central to contemporary theories of light such as the John Cramer and Ruth Kastner’s “Transactional Interpretation of Quantum Mechanics” or the Pope-Osborne Angular Momentum Synthesis. As for some old business. I was told more than once that a one-slit diffraction pattern is not an interference pattern. This was stated as a matter of fact with no explanation except that it was impossible. I explained how it is possible and considered the matter concluded until I mentioned again that a one-slit diffraction pattern is an interference pattern. That was too much “not listening” and the thread was closed. The problem is that anyone with a home-made slit and a laser pointer can get a perfectly good interference pattern from a single slit and I have done so many times as have many others so how can it be impossible? I know where the idea comes from because the nearly unanimous consensus among physicists is that it is impossible because the broad band observed when light passes through a single slit does not show any of the fine bands of light and dark characteristic of an interference pattern. What gives? For one thing, if your single slit is wide, like more than a wavelength light, and your detector is the side of the kitchen refrigerator, it is easy to see that the diffraction pattern lies of the same plane as where you would expect an interference pattern to fall. If you look beyond the end of the line in the center of the pattern you can see smaller bands of interference. There may only be two side bands visible, but if you make the slit narrower, the long band in the center becomes shorter and less apparent while the bands to the side move inward and become brighter. As the slit narrows, the diffraction looks more and more like an interference pattern. It becomes apparent that the bright band in the center is just one band of a typical looking interference pattern- which it is. The physicists must be looking at just the long bright band in the center thinking it’s the whole diffraction pattern when it is only a single band of an interference and one would not expect to find interference bands within a single band. Here is a quote from Sabina Hossenfelder and she explains this in detail. The bolded letters are mine. http://backreaction.blogspot.com/search?q=quantum+eraser+experiment “The interesting thing about the double-slit experiment is that if you measure which slit the particles go through, the interference pattern disappears. Instead the particles behave like particles again and you get two blobs, one from each of the slits. Well, actually you don’t. Though you’ve almost certainly seen that elsewhere. Just because you know which slit the wave-function goes through doesn’t mean it stops being a wave-function. It’s just no longer a wave-function going through two slits. It’s now a wave-function going through only one slit, so you get a one-slit diffraction pattern. What’s that? That’s also an interference pattern but a fuzzier one and indeed looks mostly like a blob. But a very blurry blob. And if you add the blobs from the two individual slits, they’ll overlap and still pretty much look like one blob. Not, as you see in many videos two cleanly separated ones.” Sabrina Hossenfelder Oct, 2021 If Hossenfelder calls the one-slit diffraction pattern an interference pattern, that’s good enough for me.
  13. You asked if there are any instantaneous natural processes and I mentioned entanglement. As for your drawing with a stream, I didn’t see anything instantaneous. You can watch a leaf in a stream flow up and over a hydraulic jump and that’s not instant. There is also a static energy to pressure gradient but a gradient isn’t instant either. What else is there to say? I don't see how anyone could possibly observe the time it takes two particles to become entangled. The "instant" I had in mind involves performing a measurement on one entangled particle and then timing how long it takes for the other paired particle to be influenced. The Chinese were perhaps the most recent to measure this with photons and they measured the time to be something like four orders faster than light. That could qualify as instant or too fast to measure.
  14. I consider "instantaneous" to be either without duration or having a duration too short to observe by any means. Quantum entanglement would be an example.
  15. Can you give us some examples where interactions between light and matter can't be explained as a wave. The photoelectric effect has been discussed and the discrete nature of photon termination can also be explained as a wave without recourse to the simplistic analogy of particle impact. I don't find either of these as convincing evidence for the particle nature of light or am I missing something?
  16. It is my understanding that an atom gains energy when an electron jumps from a lower energy orbit to a higher orbit and one should not think of an electron in orbit about the nucleus as having a position in space as if it were a tiny planet in orbit about a star. Electrons are best thought of as probability waves rather than having a location. I have never looked into the thinking behind the theory, but the speculation is that an electron “quantum leaps” from one orbital to the next without passing through the space between. It simply vanishes from one orbit and appears in another without a transition through either space or time so no time interval can be assigned to how long it takes an atom to gain energy.
  17. Light is in the frame of light and that is where the transition takes place. Our perception from afar is not a determining factor. Light may land within the probability predicted by energy, distance, and time. That is based on previous observations of similar events in the past but the same interpretation may not apply to the reference frame of light which lacks a time interval even though the end results are the same. And interpreting light as a particle in this case, isn’t that applying a classical model to a quantum event? And what is a “particle” in the quantum view? “When an energy exchange occurs between, say, two molecules one wonders what is traveling between them. If we don’t know, we say it is a “photon” Giving it a name doesn’t add any knowledge, but it allows us to feel better and we can pretend we know what travels.” Milo Wolff “What we observe as material bodies and forces are nothing but shapes and variations in the structure of space. Particles are just Schaumkommen.” (appearances)- Erwin Schroedinger 1937
  18. I suspect the blurred lines are a result of the uncertainity of which atom will absorb the light rather than a matter of timing. From the reference frame of light, emission and absorption are simultaneous events.
  19. I still suspect the experiment has a explanation in the polarity. The light reaching the moving detector Ds is both linear and circular because quarter wave polarizers QWP’s have a linear polarizer followed by a circular polarizer so the light reaching the moving detector is both linear and circular and beyond just circular as mentioned in the description. The description doesn’t explain the thinking behind the use of the polarizers or their orientations. That is likely to be found elsewhere but the information in the article is inadequate. Diffraction is interference with bands and all.
  20. Q:Surely both photons must be in the same frame to entangle them. A: Not necessarily. But for experimental purposes, they must originate from the same spot if we are to recognize them as entangled. In other words, if we have a single particle, we have no way of knowing if it is entangled elsewhere or not. Q: And if they are in the same frame they must be in the same frame and therefore subject to the same transformations, relative to any other frame. A: Entangled particles have no “location.” We can’t say particle A is here and B is there. The locations are said to be "indefinite" until observed. In other words, a single unobserved particle can entangle spontaneously with another particle anywhere on the same light cone. And they are subject to the conditions of their local reference frame. Q: I simply asked because you originally stated quite clearly. 22 hours ago, bangstrom said: The entire body of quantum identities can be entangled Are you suggesting that say position and momentum are not quantum properties or quantum identities (whatever they may be). ? A: Position and momentum are much the same as location. You can’t assign position or momentum to entangled particles until you can identify which particle is where and their location is indefinite until you observe the particle.
  21. That’s right but with linear polarized light the interference is so rapid and random that it is no longer apparent. Also, two linear polarizers at orthogonal angles block light but circular polarizers do not. When you have waves from one edge of a single slit and waves from the other edge and they overlap, the two waves interfere. In the case of a single quantum of light energy, the waves are said to be “probability” waves and the interference builds over time- one spot at a time. The part about linearly polarized light interfering so rapidly and randomly that interference is no longer apparent comes from Fresnel and Arago’s original paper where they introduce their three laws of polarity. The loss of interference does not happen with circularly polarized light which counters Skully and Druhl’s theory that the availability of which-path information destroys interference. In which case, which-path information is a bogus explanation. That leaves polarity as the most likely explanation for the loss of interference.
  22. When the two beams are marked with linear polarization, which-path information is available and you don’t have interference. When the two beams are marked with circular polarization, which-path information is available and you do have interference. `The two polarizations do not act the same.
  23. Momentum is observer and reference frame dependent and not part of a particle's identity and only the identity can be entangled. Identity includes such things as charge, spin, or polarity. The experiment you cited is new to me but I like the choice. It is much simpler that what I had in mind and it confirms my view that circularly polarized light makes which-path information available while continuing to produce an interference pattern. The explanation about rapid interference refers to Fresnel and Arago' first law of polarization and their explanation of how linearly polarized beams interact. It does not include circularly polarized light which is quite different. Beams of circularly polarized light do not interfere destructively as do linearly polarized light. When light waves passes by an obstruction, they fan out. They diffract. A single slit has two edges and the diffraction patterns from each edge interfere to produce a diffraction pattern which is characteristic of light as a wave. As described by Skully and Druhl, marking the two light beams with polarization makes which-path information available and destroys interference. Marking the light paths with circular polarization does the same without destroying interference contrary to Skully and Druhl but not Fresnel and Arago.. The linear polarization on the p path of your experiment is lost in passage through the two quarter wave polarizers and circular polarization is imparted. Since the beams are circularly polarized even though orthogonal, they can produce interference.
  24. I am sure the polarizers could be placed in front of the double slits but it would require a bit of micro-manipulation to position the polarizers just right because the slits are so tiny. That must be why it is never done that way. The diffraction pattern spreads widely behind the slits so it is much easier to position the polarizers to the rear. Plus you can see what you are doing. It should make no difference if the polarizers are in front of the slits or behind. I think that is what you are saying. The polarization should remain the same and the which-path information should remain the same. The question is, Why should we say the which path information information destroys the diffraction pattern when Fresnel and Arago have a perfectly good explanation for why this should happen. On the other hand, the which-path explanation sounds more than a little like new-age crystal woo so I have my doubts. The part that needs explaining is how which-path information can destroy interference. I have personally tried the experiment with circular polarizers (behind the slits) and found that circular polarizers do not destroy interference but they do provide which-path information just as linear polarizers do. This suggests that the culprit is linear polarization rather than which-path information. I haven’t found any information in the literature about what happens if one substitutes circular polarizers for linear polarizers but I have found some anecdotal reports that circular polarizers destroy interference so the matter is in doubt but I haven’t found any indication in Fresnel and Arago to indicate that it shouldn’t work contrary to the which-path theory. I don’t doubt there are several here that know more about quantum physics than I but my comment is in reference to “a single specific experimental setup.” I am just surprised that the physical setup is not better known.
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