bangstrom

Thanks for the information. I forgot about my old friend-What's his name?- Google?

This is the source of my confusion. I am not familiar with the term “plane” wave. From your later description, what you call a “plane” wave sounds like what I am familiar with as a longitudinal wave, a scalar wave, a compression wave, or generally something like a sound wave. I was trying to divine what you meant by “plane” wave in this statement,” The slit(s) experiment require a single plane wave in the space between the source and the slit(s) barrier. “ The slits usually use light as a source so the word “plane” wave must be something that applies to light such as uniform. If a plane wave is what I am familiar as a longitudinal wave, the statement makes no sense. Did you use the wrong word here? If by planar you mean planar light (longitudinal) light, I don't think there is such an animal. If by planar you mean you mean linear polarized light, there should be a dot. If by planar you mean sound waves, the dot should be there as what is called a standing wave.

I have underlined the statement I have in mind. When you say "single plane wave" I assume that means both even illumination and in the same direction and I assume by "in that space" you mean the space between the light source and the double slits. It is my observation that interference is possible and observable on a screen inserted in that space with coherent light. Specifically, with laser light because the light on the screen is not even. The light appears as many minute dots rather than uniform. The dots are too closely spaced to disrupt the interference pattern that forms after passing through the double slits but the the original, undisturbed light source is not interference free.

The particle-wave debate was largely settled in favor of a wave around 1800 with Arago’s discovery of Poinclair’s dot. The particle theory later returned to serious consideration with the success of Einstein’s explanation of the photo-electric effect. I don’t care to debate the matter at this time so I am content to remain wrong. Anyhow, it won’t be decided here. I have one point of disagreement about your discussion of light. You can’t get an evenly distributed light from an undisturbed coherent light source. Try it yourself with a laser pointer. Red works best because of its longer wavelength. The light appears as many minute dots on a screen.

I may not be following your first question correctly but interference is possible before the slit barrier and it can be observed if a screen is placed in that position to make the observation. Interference can be observed if the light source is coherent but not if the light is incoherent. For example coherent light from a laser does not appear uniform. Instead it appears as many tiny dots when viewed up close. Interference is also possible if the light has passed close to the edge of an object on the way to the screen. (a) Diffraction is obvious with a single slit and interference is possible but not so obvious as in the case of unobstructed coherent light. (b) Diffraction and interference are both obvious with a double slit. The two forms of interference converge on the same broad line perpendicular to the double slits.

Light waves and water waves are much different things. Light is a transverse electromagnetic wave unlike water. The only thing I really have to say about the particle theory of light is that it fails to explain some of the experiments involving the quantum nature of light. Specifically, the Wheeler Delayed-Choice Quantum Eraser. Since the particle approach fails, I am exploring the idea that the wave approach should work better and I am finding that it does.

I have listened to your complaint and have no intention to argue the semantics.

Light is emitted and absorbed from a single point. Its emission from a point doesn't indicate that it must be a particle and it absorption at a point doesn't mean it must be a particle. A vibrating guitar string is a point at both ends but a wave between. Light's absorption at a single point does not necessarily indicate that it was ever a particle. The statement that a 2 eV “photon” should interact with two particles having a 1 eV transition if it is a wave is a personal opinion that “swansont” has not supported with either evidence or an explanation so why should I take it as creditable? The basic is that light never acts that way.

The point at which the light is observed upon its arrival is consistent with the probability of light behaving as a wave all the way from signal to sink. I don’t consider the condition of light at the instant of its annihilation as indicative of its properties prior to that event.

My understanding is that light does deliver its energy in a localized fashion. This is why many suspect it must be a particle. Is there any evidence to support your statement that light is not localized. That is, delivering energy from one charged particle to more than one other charged particle.

I am all in favor of looking at a problem from multiple points of view but I don’t follow the physics behind your example. If an electron within an atom, can make a 2eV transition and emit a 2eV photon, why can’t a receptive atom receive a 2eV photon. That is also my understanding of how it also works with waves. I don’t understand why more than one atom must be involved in the case of waves.

Why would more than one atom need to be involved?

I see light as a wave and never as a particle. Light is quantized for certain but that does not mean it is a particle. Light is emitted and absorbed by electrons in discrete amounts representing the many differences in energy levels from one electron orbital to the next and that is why light waves appear as quanta. The photoelectric effect converts light energy into a stream of electrons but counting electrons thinking that each electron represents a photon is not a valid assumption. BTW it is not "my" discussion or even my OP. I am just another butinski.

I remember Marshall but I will have to look into what Rovelli has to say. My answer is at the bottom. In my view of the double slit experiment, the slits are detectors of nothing when light is involved. This may be a different matter with electrons. Light as a wave should pass through both slits so there is no which-path information because the light wave took both paths. The which-path information must be indicating something different. In experiments modeled after the Wheeler Delayed-Choice experiment there is a beta barium borate crystal (BBO) directly behind the double slits. The purpose of the BBO crystal is to generate pairs of entangled photons...No, forget the photons. The crystal generates entangled pairs of wavelets of light energy. In Wheeler’s Delayed-Choice, light enters the BBO crystal as an extremely powerful laser beam of UV light and it passes directly through the crystal. On extremely rare occasions, a quantum of UV energy is absorbed by a BBO molecule and an electron in one of the atoms is boosted to a much higher energy level. Instead of dropping back down to its original energy level in one big jump, the electron drops down in two steps releasing two entangled photons wavelets. If the two wavelets are of equal energy, they are called “parametric” and the whole process is called “spontaneous parametric down conversion” SPDC. I think SPDC is largely a distraction from what else is happening. The original UV light from the laser and any light except for the feeble red light having half the energy and twice the wavelength of the UV light is used for the rest of the experiment. Everything else is removed by color filters. BBO crystals are used because they are the only birefringent crystals that can survive the heat of the UV laser. The BBO crystal is a nonlinear, birefringent crystal with optical properties nearly identical to calcite. When a light wavelet enters a birefringent crystal it can take one of two paths. It can go straight through the crystal on the “p” path or it can take a slight jog to the side on the “s” path. Also, when light travels through a nonlinear crystal as an electromagnetic wave, the wave is slowed upon entry more on the electro plane than on the magnetic plane. This gives the wave an apparent spiral called circular polarization. Light can be both circularly and linearly polarized at the same time and this is the condition of light when it emerges from a birefringent crystal. I suspect the which-path information that is determined later is more likely to indicate which path the light wave took as it passed through the BBO crystal (the p or s path) than which path it took through the double slit. Other than myself, I don't know of anyone who has looked into the effect of circular polarization on the simple double slit experiment but I have read some hear-say accounts that orthogonol beams of circularly polarized light will not interfere. If they do interfere that would give you which-path information and interference at the same time which is claimed to be impossible. I have tried it and it works for me.

The double slit is evidence of light waves but it also works with particles. Small particles also have a wave nature so the two properties are not mutually exclusive. The presence of which-path information is characteristic of the particle nature of light and the presence of which-path information destroys the interference, so in experiments where which-path information appears to be critical to the outcome, light is considered to be to be acting as a particle. A wave should not be expected to demonstrate which-path information. Yes, the screen is a detector. The Wheeler Delayed-Choice experiment uses two electronic versions of a screen looking for interference. One receives light from both slits and indicates the presence or lack of interference. The other is a Mach-Zehnder interferometer that looks for both interference and which-path information. The second is located meters behind the first so interference is noted first and the which-path information is determined later.

Yes, the experiment is about which-path information and there is no evidence from the experiment to indicate that light is a particle. Light appears as a wave through out the experiment. The results that are said to be lacking interference are diffraction patterns which are just a less elaborate demonstration of wave interference. The conventional interpretations of the double slit experiments is to consider light as a particle and that approach leads to a dead end. The conventional interpretation of the Wheeler Delayed-Choice experiment is that an observer can decide the outcome of the experiment by determining the which-path information even if the determination is made after the experiment is completed. The retroactive nature of which-way information is a problem for physics. Yes, that is the way it works. There is an interference pattern when there are no detectors of which-way information but the interference pattern is lost when the detectors are present. This makes it suspicious that the detectors are causing the loss of interference. In one test of the double slit experiment, the detectors were placed behind the double slit and recorded the which-path information. This destroyed the interference pattern. The test was then repeated with the detectors active but unplugged from the recorders and the interference returned. The interference pattern is destroyed whenever the which-path information is “out there” but the interference pattern is present even when the detectors are present and active but there is no record of which-path information. This places the suspicion on the presence or absence of which-path information as a cause for the loss of interference.

This is a quote from Anton Zeilinger. “Thus, even though a sub-quantum amount of light is received at a detector, the probability of a detection event occurring at the detector increases with the amplitude of the received light signal. Thus, even sub-quantum amounts of light can cause detectors to trigger and generate “click” events. It is sufficient to destroy the interference pattern, if the path information is accessible in principle from the experiment or even if it is dispersed in the environment and beyond any technical possibility to be recovered, but in principle still ‘‘out there.’’ The absence of any such information is the essential criterion for quantum interference to appear.” A. Zeilinger Zeilinger is saying that even if the light level is so low that you have only one light event at a time passing through the double slit, a “click” of the which-path detectors is sufficient to prevent the formation of the interference pattern for as long as the “which-path” information is “out there”. However, if the which-path information is destroyed beyond recovery before you observe the results of the experiment, then an interference pattern appears. The results suggest that a person has free will to determine the outcome of the double slit experiment. If he chooses to learn the which-path information before observing the results of the results he will see no interference. If he has no means of learning the which-path information, then there will be interference. The results suggest that the interference pattern is not possible if someone has access to which-path information but interference is only possible if the which-path information is unknown and unknowable. The obvious explanation is that the which-path detectors are interfering causing the loss of interference but that possibility has been ruled out. The detectors were moved from the front of the double slit to the back with no change in the results. They were even moved all the way back so the which-path information was not determined until after the interference should have taken place but the interference pattern does not appear whenever the experiment is observed while the which-path information is “out there.” This is the difficulty behind the question in the OP. I agree with both statements. The Wheeler Delayed-Choice Double-Slit experiment is a good example to consider because it contains all the elements that are interpreted as having observer involvement- not necessarily human but possibly just sentient. I think this is the sort of explanation the OP is asking for so let it run. Sorry about the confused quotes, I am new to this forum and haven't figured out the editing yet. That short quote from "swansont" should have been at the beginning.

One question is, How do the objects that follow 'know' where to land in order to produce an interference pattern characteristic of a wave? With light, it is said that the wave becomes a particle when observed and it will no longer produce an interference pattern. This same scenario continues to say that the photon 'knows' it is being watched when a 'sentient'? observer discovers which path it took when going through the double slit and alters the outcome of the experiment accordingly. This is the interpretation of the Wheeler Delayed-Choice Double Slit experiment and it brings us back to the question in the OP. "Does the ability of an observer to affect an outcome simply by choosing to observe it mean that the choice had to have been made outside of all universal conditions?" One problem with scenario above is that, if the photon passed through just one slit, a single photon can't produce an interference pattern. If it split and passed through both slits or if it passed through both slits as a wave, there could be no which-path observation since it went through both. Also, if the wave has become a photon particle, it should produce a pattern characteristic of a particle like this || . Instead, it produces a diffraction pattern which is a long horizontal line with a few horizontal lines to the side. This is also characteristic of light as a wave. There is no evidence in any tests of the double slit experiment where light is behaving as a particle. That only happens in the cartoon illustrations of the experiment. If the above part is clear, i think I can explain how the experiment works with no human involvement.

The delayed choice double slit quantum eraser has EVERYTHING to do with optics. What happens when you send an electron through a BBO crystal or a C-60 molecule through a polarizing filter? It only works with light.

I am saying the which-path information is not telling us which way the photon went through the double slit but something else. Most likely it is telling us which slit the transverse light wave went through on the dielectric plane. I am also saying the absence of an interference pattern was explained in classical physics by Fresnel and Aragon and it has nothing to do with our observation of which-path information. I have not yet explained how the electrical observation of the photon path applies, but similar to observations with polarized light, the Delayed Choice Quantum Eraser can be explained as involving the combined effects of both linear and polarized light emerging from the birefringent crystals. This is no different from the technology used for the modern type of 3D movies.

OK And I see no collapse of the wave function. A paper by Fresnel and Arago (see Fresnel-Arago Laws) published two centuries ago explained why orthogonal polarized lights do not produce an interference pattern. The two beams collide in such a way that the interference is so rapid and random that the light is no longer coherent and the interference is no longer discernible. This has nothing to do with which-path information. I have found that light “marked” with circularly polarized light does produce an interference pattern so it is possible to have which-path information and an interference pattern both. This is consistent with the observations of Fresnel and Arago. There is no indication of a collapse of the wave function at any point in the double slit experiment,so even at low light levels where the light signal becomes intermittent and is observed as quanta of energy, there is no evidence to support the idea that light has become a particle. A quantum of energy can have the form of a wave packet and is not necessarily a particle. The classical view of the double slit experiment holds that light passes through both slits and both beams fan out and produce an interference pattern on the back side. The photon theory of light offers a more speculative view where a photon particle splits in two and passes through both slits and then both particles become waves that interfere with each other on the other side. Neither of these scenarios is consistent with the later determination of which-way information where the photon is observed to pass through only one of the two slits. So what can be passing through one slit but not the other? Light waves are transverse electromagnetic waves as discovered by Fresnel. One wave lies on the dielectric plane and the other is on the magnetic plane. When light passes through a birefringent crystal it is refracted upon entry into two divergent paths. One path is diverted more strongly than the other because the light wave on that path is slowed more on the electric plane than on the magnetic plane. This gives the transverse wave an apparent spiral. The two light paths that emerge from a birefringent crystal are oppositely polarized both linearly and circularly. In the “Wheeler Delayed Choice Double Slit Experiment” there are two color filters and three birefringent crystals directly behind the double slit. The first birefringent is the BBO crystal and the other two are found in the Glen-Thompson prism. These are usually calcite crystals. I suspect that the later determination of which-path information in the Wheeler DCE is not telling us which slit the photon went through but which path the light went through on the dielectric plane. And since the light in the experiment is second hand light generated within the BBO crystal, (not the UV light from the laser) it may not even be telling us which slit the original light from the laser went through. Sorry about the font size. I don't know how to change it or why it didn't go to default size.

I am interested in knowing if anyone can repeat my modification of the "DIY Quantum Eraser Experiment". Directions for how to perform the experiment can be found on YouTube. My modification involves replacing the two linearly polarized films in the experiment with two circularly polarized films to see what happens. I have observed that marking the two light paths with circularly polarized light does not erase the interference pattern contrary to the which-path theory. Ordinary clear cellophane tape "Scotch tape" serves well as a circular polarizing film and the tapes become orthogonal at a 45 degree angle. The tapes can be applied to glass for support. A microscope slide is ideal. The correct polarizing angle can be verified by examining the films sandwiched between two linear polarizing films or better by examining the films through polarized glasses when backlit by light from a flat screen LCD monitor. Quote from wiki: “However, in 1982, Scully and Drühl found a loophole around this interpretation.[11] They proposed a "quantum eraser" to obtain which-path information without scattering the particles or otherwise introducing uncontrolled phase factors to them. Rather than attempting to observe which photon was entering each slit (thus disturbing them), they proposed to "mark" them with information that, in principle at least, would allow the photons to be distinguished after passing through the slits. Lest there be any misunderstanding, the interference pattern does disappear when the photons are so marked. However, the interference pattern reappears if the which-path information is further manipulated after the marked photons have passed through the double slits to obscure the which-path markings. Since 1982, multiple experiments have demonstrated the validity of the so-called quantum "eraser"” I have always been more than a little dubious about the theory that "which-path" information can alter the results of an experiment and the Fresnel-Arago Laws explain the experiment so much better without the quantum woo.

I think we are saying the same thing. I understand the evolution of the universe as a several billion year emergence from a gravity well with the BB at the very bottom.

No, it is still possible to use rotation to create artificial gravity. The point is that an object floating free in the depths of space is still within the effects of the gravity originating from the sum of all the massive bodies in the universe. This gravity determines our perception of distance and time. There is no place in the universe that is free of gravity.

I suspect the general enlightenment about gravity is little better now than it was in Einstein’s time and the popularity of the flat earth theory makes me wonder if has gone the other way. Einstein’s delight in the Equivalence Principle was in knowing that he had discovered two ways of thinking about the same problem so he could test his theories about gravity against his understanding of free fall looking for consensus between the two. More importantly, the Equivalence Principle gave him simple examples he could use to explain his ideas to others. Everyone knows that astronauts are weightless in space but it is my impression that popular opinion holds that there is no gravity in space and I don’t think it is generally understood that astronauts are subject to much the same gravity as we are on the surface of the Earth. The difference between us and the astronauts is that they are in continuous free fall. There is also an erroneous impression that there is no gravity in deep space far from any massive bodies. Einstein’s Equivalence Principle seems to be less difficult to comprehend than what Einstein called Mach’s Principle which deals with universe wide influence of gravity and it is the latter that is the most enlightening about gravity.