Physicists Modify Double-Slit Experiment to Confirm Einstein"s Belief, Full story at http://www.physorg.com/news92937814.html

http://www.physorg.com/news92937814.html

It appears Afshar has misinterpreted the Copenhagen interpretation. From what I see in this article, it appears Afshar and friends believe that the Copenhagen interpretation says that light sometimes behaves as a particle and sometimes a wave. That is not the interpretation. The interpretation is this: you can"t detect both types of behavior in a single event (single "experiment"). For example, you can detect wave behavior in the statistics of multiple photons, and you can detect particle behavior in a single photon. There is nothing surprising or revealing about Afshar"s experiment.

-fleem

Yeah, this is unintuitive. They "Simultaneously" measure the presence as a particle and failed to measure it at the wave. In the QFT view of the photon, this result is always expected, and I don't see where this experiment leads to new physics at all.

http://arxiv.org/abs/quant-ph/0702188

The "Logical inconsistency" is in trying to use classical concepts of particles or waves at all. I thought from reading Baez and the like, we were all well-past this hump.

Explanation is simple: photon goes through both slits as a wave and interferes with itself, then when the photon is detected and collapses into a particle, its history also collapses into that of a particle and from the detector's point of view it originated from just one slit. The wires play their role prior to that detection, therefore they imply the photon is a wave as expected because it has not yet collapsed upon passing them.

Sure, that the past can collapse upon observation in the present seems like some violation in the arrow of time, but just like superluminal interactions between entangled particles it cannot be used to send information, so no problem.

Also, I call into question the wires being placed at the dark fringes. That is where the wave amplitude is zero. Something placed at zero wave amplitude cannot possibly interact with the wave because there is no wave there. Perhaps it seems to violate convention only because it is a special case that has no practical bearing on the Copenhagen interpretation just as the gravity field of zero mass has no bearing on celestial mechanics.

I saw pictures of Afshar's experiment in Discover Magazine, and the interference fringes he got with the wires blocking the dark fringes and the picture of the experimental result without the wires was discernibly different. Where is he publishing his new experiments?

I provided the correct interpretation of quantum mechanics one year ago:
astro-ph/0604084.

People (Nottale, etc.) know that the distribution of planetary distance in solar system can be explained by Hydrogen wave function accurately. However, no one believes that there is macro-phenomena of quantum mechanics. Two reasons of macro-quantum mechanics:

1) What is the interpretation of quantum waves for solar system? My explanation is simple: single particle is always particle! Therefore, in micro-world, single particle is always particle! If the size of a person could be reduced in the one of an atom then he would see my conclusion is correct!! However, the macro-sizes of human and their instruments disturb micro-particles and my conclusion is not obvious. The wave function is still the probability interpretation of Born: distribution of many particles in the same environment. That is, classical mechanics describes particle motion of single particle while its quantization describes the spatial distribution if there are many particle in the same classical condition. It is true for both macro and micro particles.

2) Is there the difficulty of Planck constant? No. My theory of covariant quantization (time and space in equal footing) has no such difficulty of Planck constant, which constant is believed by mainstream people to refuse macro-quantization. See astro-ph/0604084.

Then that WOULD be revolutionary (or more likely be evidence of a mistake in the experiment!). The article here on physorg didn't mention that--or else I missed it.

On a side note, here's a fun thing you can do with duality:

Split and then recombine a laser beam such that you get destructive interference in the final beam (i.e. there is no resultant beam).

This is effectivley like adding a dielectric mirror at the front of the laser, and reflects all energy back into the laser.

Now turn down the power until you can count individual photons. You'll not count any, of course, because of the destructive interference.

Now block one of the split beams such that the destructive interference goes away.

Start counting photons!

So by placing a block of wood in one path, you allow light particles to go along the other path.

Pretty cool, eh?

-fleem

I've always been told that wave interference occurs when two out-of-phase waves cancel each other out, leaving a dark fringe, and two in-phase waves reinforce each other, producing a bright fringe. Conservation implies that two waves continue on past the dark fringe, rather than ceasing to exist at the point of interference. Given the placement of the absorbing wires at the black fringes where they don't reduce the subsequent intensity of the light, it seems that the photons don't interfere with each other by opposing each other's phase to cause a dark fringe at that point. It seem more like the photon particles interfere with each other by directing each other's paths into the bright fringes and away from the dark fringes. Thus the dark fringes can be made without blocking any of the photons or reducing any of the intensity of the light. To clarify this idea further, this seems to imply that each single photon passing through a double slit has its path changed by passing through the slit in such a way as to be sent to a light fringe and not to a dark, thus producing light and dark fringes without reducing the intensity of the light. So maybe the wave is just a euphemism to explain a specific and consistent spray pattern of particles.

This `article' betrays the bad physics it discusses. First, this is a press release from Rowen University, not an independent journalist. Second, a common, clear give-away is the repeated insistance that "this work has been accepted in a reputable journal". There's no need for such statements when it's good science, and is usually used when the mainsteam of scientists do not consider the work to be good. And third, if you know anything about the subject "interpretation of quantum mechanics", the discussion and claims in the press release is weak. There have been real advances in our understanding via experiments of the past few decades. For discussion of these, see Roland Omnes' "Understanding Quantum Mechanics" or more recenty "Consistent Quantum Theory" by Robert Griffiths.
Cheers (and jeers).

One cannot say if the photon, when passing the slits at the time T0 is a wave or a particle.
One can indeed say that it forms fringes as a wave would do, at some distance from the slits and at time
T1. If then, at another, larger distance, at time T2, the photon is detected by a detector, then one may say it has seen a particle. By putting the wire in the place where zero intensity is expected does not subtract flux to the wave. It would be more interesting if one compares what happens when the wires are displaced (i mean: does the absorption of some flux implies that you see/you don't see the photon?)

Claiming that the complementarity principle is wrong on the basis that in the same _apparatus_ you have either the wave and the particle aspects is not correct. Causality and reductionism implies that you have to take the fringes at time T1 and the detector at time T2 as TWO DIFFERENT subpart of an experiment in which the nature or light is of a well defined character, either wave at T1 *OR* particle at T2.javascript:emoticon(':angry:')

Complementarity principle seem to be saved, no matter what Einstein and this guy say. It seems to me that too many people are obsessed in proving that Einstein was right or wrong, just because they want to clothes themselves with the aura of doing something in line with the work of the world-most-recognized genius. They would live better and add much more to our society by trying to concentrate on more solid and perhaps more original lines of thinking.

Isn't the wave particle duality an artifact of the fact that the waves are quantized? Like the toy Newton's Ladder, where a shock wave is quantized by the number of balls initially pulled back. Photons are quantized because they are generated by some physical process that creates them and measured by a physical process that interacts with them. As alternating self regenerating electric/magnetic fields they may have a center of motion but will interact with other objects in the universe according to the formulas describing the electric and magnetic forces. The fact that "particles" also show duality is only a confusing because of the delusion whereby we mentally associate solidity with the property of mass.

Well, I finally got a chance to read the paper and I take back my first complaint that these folk didn't understand Copenhagen. They clearly and correctly describe complementarity in the paper. So I now admit they do understand it. (I was relying on the physorg article, which didn't well describe the paper). However, I still have trouble picturing their setup from their text description. I feel I've missed something. They needed a diagram! So likewise I can't see how they "inferred" wave behavior for a single detected photon.

So I'm still convinced the claim they make is incorrect. The energy you get when you absorb a photon is always exactly enough to tell one thing about the photon. If that were not the case, then there would have to be some other type of energy transfer that DID only have enough energy to tell one thing about it, but we've detected no interaction more fundamental than a photon. I'm not saying this is proof of complementarity, I'm just saying it would be strange that a "more fundamental" form of energy transfer has been able to hide from us so long.

I've always felt it is a mistake to teach that particles "sometimes act like classical waves and sometimes like classical particles". Ever see a classical particle sometimes look like a wave, or a classical wave sometimes look like a particle? No! As Feynman quips, "there's no such thing as classical, dammit!"

Therefore photons are neither. They are something else entirely. This preoccupation with thinking of them as classical wave/particles has, IMO, hindered us from understanding their true nature.

Certainly we can admit there are similarities. I'm just saying we have to be careful to remember the analogies are only analogies.

Take a look at this USENET post:

http://groups.google.com/group/sci.physics...4abf1259?hl=en&

This is not new! At the end of the 1980's, three Indian scientist, Dipankar Home, Partha Ghose and Girish Agarwal, performed a similar experiment with a beam splitter(tunnel effect). So did Yutaka Mizobuchi and Yoshiyuki Ohtake. So did ......... and the list goes on. We conduct countless experiments and observations, but still don't have a clue about (The Strange Theory of Light and Matter).

There is one simplification at least. Electrons behave in this respect in exactly the same way as photons; they are both screwy, but in exactly the same way.

-Richard Feynman

I know I can safely say than nobody understands quantum mechanics ... Do not keep saying to yourself ... "But how can it be like that?" because you will get "down the drain," into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.

-Richard Feynman

I believe the photons are best represented as particles (though not necessarily travelling through the space between an emitter and detector - they simply convey information that we use statistical features of and interprete these, possibly artificially created, statistics to measure spacial dimensions/distances). So the wave characteristics most likely arise, not from an inherent wave property of the photon, but a wave property in our understanding/construction of space. This doesn't give a clear picture exactly what's happening but here's an analogy.

Imagine that the experiment itself is moving, instead of the photon.

Let's say the universe was filled with many springy and resonant structures (along with many non-resonant ones, but those are just chaotic background now) and you happen to grab one of these and call it "matter".

If you're vibrating back and forth with some specific frequency and amplitude, the only objects that would appear coherent would be ones possesses the same phase, frequency and amplitude as yourself. Anything else would appear wavelike (if it vibrated at the same frequency but phased differently, or at a slightly different amplitude), in an orbital motion (if the frequency was slightly different than yours) or chaotically unpredictable "virtual particle" (if it didn't resonant at a constant frequency and/or amplitude ... or simply if it diverged enough to be difficult to determine the motion).

In this case, you could see the twin slit experiment as a spacial filter that only allows specific phases and amplitudes of photons to pass through it. Does anyone have information on the attentuation of the amplitudes of light passed by the twin slit experiement? Does it pass more than double the number of photons of a single slit? The waves could be seen to arise as much from the matter used in the experiment as the photon itself - after all, if we dig down into mass and find no hard center, why should matter remain stable (I don't believe it does, and that's why things diffuse outward and bump into each other - of course you can't see it easily if you're expanding/diffusing along with this).

The question is over how we detect one direction in space as being different from another? If you were drifting in space with no external references around - we could assume you'd still be able to point one arm in one direction, and another arm in the "other" direction ... what fundamental property(s) of space or mass allow for this distinction to be made? At a minimum it appears we need 3 independent attributes availabe in order to see properties as 3 dimensional.

Take a television and look at how the picture is constructed. The informaiton begins as a serial stream of information that doesn't directly exist as a 2 dimensional image over time (or 3 dimensions total).

So how does a television extract the other 2 dimensions from this signal? It detects "sync" markers that slice the information into separate lines and then sweeps down the screen vertically and then when it hits the bottom, it detects another marker that makes the beam retrace back to the top and it starts over.

This could also be seen as an analogy of a mail sorter, matching zip codes and placing the appropriate envelopes in different pathways - but it's easy to see what properties allow for mail or television scan lines to separate information into different "dimensions". It's not as easy to look at yourself and know what aspects of "matter" you're detecting for spacial locations.

Because of this vibration, you could have two areas of space that might appear different be truly close together in some fundamental sense, because you could be construsting an artificial measure of distance in order to distinguish between properties of various things but overlooking other properties at other phases, frequencies, periods or amplitudes, or even chaotic ones without any simple sinusoidal motion involved.

In this way you could take a single particle and have it appear to exist in multiple places at the same, not because it fundamentally must, but because your perceptions are "synced" to different features of space that create aliases of it. (For example, from the perspective of a photon in this experiment, all paths could have appeared to be a single straight line, and this seems the only way it could see it if time dilation under relativity is accurate - it had no way of seeing where it was going so it left the emitter at the same instant it was hitting the detector, form its perspective, it would have no time to run an obstacle course, so we must be imposing our own view of time upon its "path", which may not even exist as a line through space in the typical sense, because photons or at least kinetic energy constructs our understanding of space).

This post has been edited by StevenA on Mar 14 2007, 04:12 AM

Hi All,

I have always been told that absence of evidence is not evidence of absence. However the converse is also true... you cannot prove existence of a property with a null reading. Any non-existing thing has a null reading for its properties by definition. This is supposed to be science. Since when did a null reading prove the existence of a property? To prove any property ... in this case the simultaneous wave and particle nature of individual photons... you must show that the same entity is being measured at the same time. Tell me has Shahriar S. Afshar proven beyond all doubt that for the one single photon, are we measuring its particle and wave nature simultaneously? The null reading in the nodes tells us nothing about a light flash on some other part of the screen. How are these connected? Why are they supposed to represent the same photon? Is there any photon in the blank areas of the screen anyway?

Quantum theory suggests that if you collapse the state of a single photon you can read "the flash" on the screen, but since the wave no longer exists anywhere else, a null result elsewhere tells us nothing. The only information that exists is where you found the tiny flash. The same principle applies to electrons as well... the null points are simply null points .... "No reading" can be made in a lot of places in the Universe, does that mean that this photon was there too?

It is totally unconvincing to me. Seems Journals will print anything nowadays.

Cheers

This post has been edited by Good Elf on Mar 14 2007, 12:57 PM