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Thread: Protons and Electrons are just like photons?

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    Protons and Electrons are just like photons?

    This is news to me, but apparently Protons and Electrons are just like Photons in their Particle/wave properties?

    In a double slit experiment a proton will act just like a Photon and go thru both holes?

    I am confused by this article. Can somone make sense of this? Please, and thank you.


    http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html

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    Yes, all particles will exhibit that type of behavior. The history of waves is interesting-- at first, it was thought that waves were an excitation of a medium, like sound waves in air or water waves on water, and so waves were something totally different from particles. But then with relativity, it was discovered that light had wave properties without the need for a medium (there was no need for an aether), and it also had particle properties (like the photoelectric effect). That was the birth of wave-particle "duality." Shortly after that came an even bigger surprise-- all particles are governed by wave mechanics, and none of them need a medium. So now, we can view sound waves and water waves as merely an analog for this vastly more general type of wave, and waves and particles are not two different things: waves tell particles where they are allowed to go.

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    It actually goes to the extreme that you, me, the earth and the moon, all have wave/particle duality.

    But as the mass increases the superposition decreases.

    Thus, for a very small and very light particle the superposition can be very spread out. But for something of a common world size, the superposition is so small that it is for all intents and purposes, not something that has any measurable effect.

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    Quote Originally Posted by Ken G View Post
    Yes, all particles will exhibit that type of behavior. The history of waves is interesting-- at first, it was thought that waves were an excitation of a medium, like sound waves in air or water waves on water, and so waves were something totally different from particles. But then with relativity, it was discovered that light had wave properties without the need for a medium (there was no need for an aether), and it also had particle properties (like the photoelectric effect). That was the birth of wave-particle "duality." Shortly after that came an even bigger surprise-- all particles are governed by wave mechanics, and none of them need a medium.
    I think this answer is appropriate for a first contact with this kind of puzzling questions, which seems to fit to the OP question level. But I wonder if it could be a little misleading in the light of the modern view of these questions we get from QFT.
    It is accepted among quantum and condensed matter physicists that the vacuum can be considered a kind of substance or matter phase with a whole lot of properties that confirm this nature of the vacuum, and in this sense it can be considered a medium for waves.
    The fact that this view is not very popular among some physicists and that no conclusions are drawn from this understanding is IMO that the conclusions might be controversial and there is huge resistance to such changes, another reason explained in the book I cite below is the possible confusion with the taboo concept of ether of the 19th century. But concepts like effective-action, vacuum expectation values, vacuum state (zero-point energy). etc have been in use for many decades.
    Probably the clearest account of these issues in popular science books are in the works of two brilliant recent Nobel prize winners in physics:
    Bob Laughling's:A different universe, mainly in the chapter "spacetime structure", and Frank Wilczek "The lightness of being" in its chapter 8.
    And in technical terms there is:"Probing the quantum vacuum: perturbative effective action aproach in quantum electrodynamics and applications" by Dittrich and Gies.

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    Here is an interesting quote:

    If [wave-particle/double slit] seems very mysterious, you are not alone. Understanding what is going on here is in some sense equivalent to understanding Quantum Mechanics.... Feynman admitted that he never understood Quantum Mechanics. It may be true that nobody can understand Quantum Mechanics in the usual meaning of the word "understand."

    This webpage appears to be a more comprehensive, helpful explanation: The Feynman Double Slit
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Staticman View Post
    I think this answer is appropriate for a first contact with this kind of puzzling questions, which seems to fit to the OP question level. But I wonder if it could be a little misleading in the light of the modern view of these questions we get from QFT.
    It is accepted among quantum and condensed matter physicists that the vacuum can be considered a kind of substance or matter phase with a whole lot of properties that confirm this nature of the vacuum, and in this sense it can be considered a medium for waves.
    No, the vacuum is not thought of that way in QFT. It is thought of as a kind of seething sea of virtual particles, true enough, but the virtual particles can hardly be thought of as a medium for waves, as they were not even dreamed of in the day when people thought waves needed a medium-- they are a new idea intended to replace the concept of a medium. Granted, if you are inclined to force the modern thinking into the old language, you might be tempted to call it some kind of "generalized medium", but I see no value in the concept-- better to simply move on and leave the medium concept behind altogether. The key point is that the older type of waves that require a medium should be relegated to a kind of second-class wave status-- those never really were fundamentally what waves are, they were just the way we encountered the concept, nothing more than a kind of ponderable analog to the more fundamental version that comes up in quantum theories. I don't think it would be very accurate to say that a sound wave is to air molecules like a light wave is to virtual photons, the way the two come up in the mathematics of wave propagation is completely different.
    The fact that this view is not very popular among some physicists and that no conclusions are drawn from this understanding is IMO that the conclusions might be controversial and there is huge resistance to such changes, another reason explained in the book I cite below is the possible confusion with the taboo concept of ether of the 19th century.
    The problem with the aether is not that it is taboo, it is simply that it is useless. There is no need to postulate an aether, unless one clings to the old and discredited idea that waves require a medium. Indeed, if you forget about light for a moment, and just think about particles with rest mass, the need for an aether becomes even more clearly superfluous.

    But concepts like effective-action, vacuum expectation values, vacuum state (zero-point energy). etc have been in use for many decades.
    Certainly. And none of those have anything to do with waves propagating in a medium. All you are saying is that vacuum is not considered to be nothing, which is a completely orthogonal issue to waves in media. Instead, it means there are several things going on in a vacuum-- wave propagation, and virtual-particle effects. One might even say that the virtual particles propagate in the vacuum.
    Probably the clearest account of these issues in popular science books are in the works of two brilliant recent Nobel prize winners in physics:
    Bob Laughling's:A different universe, mainly in the chapter "spacetime structure", and Frank Wilczek "The lightness of being" in its chapter 8.
    Again, both about the surprising properties of vacuum, not about waves needing a medium like sound in air.
    And in technical terms there is:"Probing the quantum vacuum: perturbative effective action aproach in quantum electrodynamics and applications" by Dittrich and Gies.
    Effective action also has nothing to do with a medium to "carry" the wave function. Indeed, the wave function is not even considered something real that would need to be "carried" by anything, it is now viewed as an abstract mathematical concept. What medium does one need to propagate an abstract mathematical concept? The vacuum has an influence on the propagation of a mediumless abstract mathematical construct-- that's the step forward, not the step back into saying that waves require a ponderable medium. The main issue is that a medium has a rest frame, and the vacuum does not.

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    Quote Originally Posted by Staticman View Post
    Probably the clearest account of these issues in popular science books are in the works of two brilliant recent Nobel prize winners in physics:
    Bob Laughling's:A different universe, mainly in the chapter "spacetime structure", and Frank Wilczek "The lightness of being" in its chapter 8.
    Yes and yes. Thanks for the update, Staticman, which one might add is still in progress.
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Ken G View Post
    No, the vacuum is not thought of that way in QFT. It is thought of as a kind of seething sea of virtual particles, true enough, but the virtual particles can hardly be thought of as a medium for waves, as they were not even dreamed of in the day when people thought waves needed a medium-- they are a new idea intended to replace the concept of a medium. Granted, if you are inclined to force the modern thinking into the old language, you might be tempted to call it some kind of "generalized medium", but I see no value in the concept-- better to simply move on and leave the medium concept behind altogether. The key point is that the older type of waves that require a medium should be relegated to a kind of second-class wave status-- those never really were fundamentally what waves are, they were just the way we encountered the concept, nothing more than a kind of ponderable analog to the more fundamental version that comes up in quantum theories. I don't think it would be very accurate to say that a sound wave is to air molecules like a light wave is to virtual photons, the way the two come up in the mathematics of wave propagation is completely different.
    The problem with the aether is not that it is taboo, it is simply that it is useless. There is no need to postulate an aether, unless one clings to the old and discredited idea that waves require a medium. Indeed, if you forget about light for a moment, and just think about particles with rest mass, the need for an aether becomes even more clearly superfluous.

    Certainly. And none of those have anything to do with waves propagating in a medium. All you are saying is that vacuum is not considered to be nothing, which is a completely orthogonal issue to waves in media. Instead, it means there are several things going on in a vacuum-- wave propagation, and virtual-particle effects. One might even say that the virtual particles propagate in the vacuum.
    Again, both about the surprising properties of vacuum, not about waves needing a medium like sound in air.
    Effective action also has nothing to do with a medium to "carry" the wave function. Indeed, the wave function is not even considered something real that would need to be "carried" by anything, it is now viewed as an abstract mathematical concept. What medium does one need to propagate an abstract mathematical concept? The vacuum has an influence on the propagation of a mediumless abstract mathematical construct-- that's the step forward, not the step back into saying that waves require a ponderable medium. The main issue is that a medium has a rest frame, and the vacuum does not.
    Well, I have to refer you to the chapters I cited above, I understand your arguments but they are responding to a number of things I didn't say, and therefore I can't debate you those since we are basically in agreement. In this case you might have some preconceived ideas about what I mean by vacuum as a form of matter, but I'm basically quoting the words of 2 highly respected scientists, this is not old physics, is more of a prejudice-less account of current physics.
    For instance when Wilczek remarks thru his book several times that the vacuum field (or the Grid" as he calls it) weighs, how would you interpret it and what conclusions could you draw from it? This is not old physics at all.
    If you think I'm misinterpreting, please say it, but I don't think so. Perhaps it all comes down once again to semantics. How would you define "medium"? I think a medium in physics can be understood as some material substance, accordin to wikipedia is :" any material substance which can propagate waves or energy", well we know the vacuum field carries energy, now you have to define matter and then you realize that is a tricky definition, according to wikipedia again:" A common way of defining matter is as anything that has mass and occupies volume.[3] In practice however there is no single correct scientific meaning of "matter," as different fields use the term in different and sometimes incompatible ways." But if the vacuum weighs and certainly occupies volume, you tell me why should Robert Laughling for instance be wrong to call the vacuum a form of matter (certainly different from fermionic matter).
    I thnk it all comes down to decide if the vacuum fulfills the required properties to be called a medium, I haven't made up my mind yet, But the arguments of the Nobel winners are very good, if you opine differently or think I'm misunderstanding, I'll be delighted to read your arguments. But remember we are not talking here so much about hte mathematical abstract wave function representation but about physical(measurable) properties, not so much about the non-relativistic Schrodinger wave function as about fields of QFT, and whether the vacuum can be considered a medium in the physical sense.

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    Quote Originally Posted by Ken G View Post
    The main issue is that a medium has a rest frame, and the vacuum does not.
    Hmm, wouldn't you call the CMB blackbody radiation a sort of vacuum rest frame?

    In case someone thinks this goes against relativity, here is from the FAQ of a Brituish Columbia university page about physics:

    Quote
    "How come we can tell what motion we have with respect to the CMB? Doesn't this mean there's an absolute frame of reference?
    The theory of special relativity is based on the principle that there are no preferred reference frames. In other words, the whole of Einstein's theory rests on the assumption that physics works the same irrespective of what speed and direction you have. So the fact that there is a frame of reference in which there is no motion through the CMB would appear to violate special relativity!
    However, the crucial assumption of Einstein's theory is not that there are no special frames, but that there are no special frames where the laws of physics are different. There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe. But for doing any physics experiment, any other frame is as good as this one. So the only difference is that in the CMB rest frame you measure no velocity with respect to the CMB photons, but that does not imply any fundamental difference in the laws of physics." Unquote

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    Quote Originally Posted by Arcane View Post
    This is news to me, but apparently Protons and Electrons are just like Photons in their Particle/wave properties?
    In a double slit experiment a proton will act just like a Photon and go thru both holes?
    I am confused by this article. Can somone make sense of this? Please, and thank you.

    http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html
    These waves that particles produce are called De Broglie waves, named after Louis De Broglie. De Broglie himself believed these waves that matter particles produced were physical waves. His related statement was:

    "When in 1923-1924 I had my first ideas about Wave Mechanics I was looking for a truly concrete physical image, valid for all particles, of the wave and particle coexistence discovered by Albert Einstein in his "Theory of light quanta". I had no doubt whatsoever about the physical reality of waves and particles."

    "In my view, the wave is a physical one..."

    "For me, the particle, precisely located in space at every instant, forms on the v wave a small region of high energy concentration, which may be likened in a first approximation, to a moving singularity."

    "I called this relation, which determines the particle's motion in the wave, the guidance formula. It may easily be generalized to the case of an external field acting on the particle."

    Using De Broglie's interpretation the double slit and other related experiments are very easy to understand. The wave enters all available slits. The 'particle' enters a single slit. Upon exiting the slits, the waves create interference which 'acts upon the particle' exiting a single slit, causing the direction the particle travels to be altered.

    De Broglie's interpretation was and is contrary to most present interpretations of quantum mechanics so his views of particle waves as being physical, created by the particle, and coexisting with the particle, have always been a minority view since his first discovery of these waves and explanations of them. Some theoretical physicists still favor his explanations and some are just re-discovering them as mentioned by Staticman above.

    http://www.natscience.com/Uwe/Forum....lit-experiment

    For the presently preferred quantum mechanical interpretations/ explanation of particle waves see Ken G's posting.
    Last edited by forrest noble; 2010-Dec-25 at 06:52 PM.

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    Quote Originally Posted by Staticman View Post
    Hmm, wouldn't you call the CMB blackbody radiation a sort of vacuum rest frame?
    No. The CMB does not appear to interface with the laws of physics in any way at all-- they appear to be nothing but an arbitrary boundary condition. Remove it tomorrow and no laws of physics change in any way, so far as we know. An actual rest frame for the vacuum must appear in the laws of physics, not in an arbitary boundary condition-- that's the difference between a true "rest frame of the vacuum", and simply a coordinate of convenience. It might someday turn out that the CMB is more than that, but that day has not yet come.

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    Quote Originally Posted by Ken G View Post
    No. The CMB does not appear to interface with the laws of physics in any way at all-- they appear to be nothing but an arbitrary boundary condition. Remove it tomorrow and no laws of physics change in any way, so far as we know. An actual rest frame for the vacuum must appear in the laws of physics, not in an arbitary boundary condition-- that's the difference between a true "rest frame of the vacuum", and simply a coordinate of convenience. It might someday turn out that the CMB is more than that, but that day has not yet come.
    Oh, but interface with the laws of physics it does, at least with those of optics, if you care to read section 5.2 of the abovementioned book by Dittrich and Gies, especially pages 187 and 188,(it can be seen in amazon.com free view) they show that photons are affected by the CMB blackbody radiation for Hubble length magnitude paths. Wich means that at that scale the vacuum is optically thick. Please correct me if that is not implied there, I'm sure you'd know better than me.

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    You don't understand. The presence of the CMB is certainly physically real, that's why it shows up in our telescopes. But that does not mean it is part of the laws of physics. The CMB is just a boundary condition-- that's how physics works, you take the laws, which in some sense "have to" be true, and then you plug in some particular boundary condition relevant to the problem at hand. So far our view is that the laws of physics are something independent from the particulars of the CMB, and that's why the CMB does not define a rest frame for the vacuum that is anything but a convenient coordinate choice for treating that particular boundary condition. Someday a theory might be generated where there is an actual rest frame for the vacuum, and it may or may not correspond to the CMB frame-- that's all idle speculation at this point.

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    Quote Originally Posted by Staticman View Post
    Perhaps it all comes down once again to semantics. How would you define "medium"? I think a medium in physics can be understood as some material substance, accordin to wikipedia is :" any material substance which can propagate waves or energy", well we know the vacuum field carries energy, now you have to define matter and then you realize that is a tricky definition, according to wikipedia again:" A common way of defining matter is as anything that has mass and occupies volume.[3]
    Yes, I agree it is an issue in semantics. I am happy with the Wiki language-- a medium is matter, and virtual particles are not matter. However, one can certainly imagine that virtual particles cause the vacuum to be a kind of "generalized" medium, I think one may imagine these things in many ways. I'm just saying that our idea of "what is a wave" has changed a lot rather recently, pursuant to the OP question.

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    Quote Originally Posted by Ken G View Post
    You don't understand. The presence of the CMB is certainly physically real, that's why it shows up in our telescopes. But that does not mean it is part of the laws of physics. The CMB is just a boundary condition-- that's how physics works, you take the laws, which in some sense "have to" be true, and then you plug in some particular boundary condition relevant to the problem at hand. So far our view is that the laws of physics are something independent from the particulars of the CMB, and that's why the CMB does not define a rest frame for the vacuum that is anything but a convenient coordinate choice for treating that particular boundary condition. Someday a theory might be generated where there is an actual rest frame for the vacuum, and it may or may not correspond to the CMB frame-- that's all idle speculation at this point.
    I'm sure there is a lot I don't understand, what you have answered now I think I understood the first time you said it in the previous post. But there are other sound sources besides your opinion, concede me that, that is why I referred you to them for this specific point , I would really appreciate it if you took a look at it and correct me if I err, or tell me exactly why this type of interaction descrribed in the text would not be part of the laws of physics.
    Thanks

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    Quote Originally Posted by Ken G View Post
    Yes, I agree it is an issue in semantics. I am happy with the Wiki language-- a medium is matter, and virtual particles are not matter. However, one can certainly imagine that virtual particles cause the vacuum to be a kind of "generalized" medium, I think one may imagine these things in many ways. I'm just saying that our idea of "what is a wave" has changed a lot rather recently, pursuant to the OP question.
    I agree.

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    Quote Originally Posted by Staticman View Post
    I'm sure there is a lot I don't understand, what you have answered now I think I understood the first time you said it in the previous post. But there are other sound sources besides your opinion, concede me that, that is why I referred you to them for this specific point , I would really appreciate it if you took a look at it and correct me if I err, or tell me exactly why this type of interaction descrribed in the text would not be part of the laws of physics.
    Any interaction the CMB has with anything else is going to be governed by the laws of physics, but that does not mean that the CMB, or its reference frame, appears explicitly in the laws of physics. Anything that happens to you or I in our lifetimes is part of the laws of physics too (speaking generally about the "laws", not intending the full-scale philosophical ramifications of that claim), but we don't appear in those laws either, and neither does our reference frame.

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    Quote Originally Posted by Ken G View Post
    The CMB does not appear to interface with the laws of physics in any way at all-- they appear to be nothing but an arbitrary boundary condition. Remove it tomorrow and no laws of physics change in any way, so far as we know.
    Well, Isn't that what Staticman said in quoting from that British Columbia university page about physics:

    However, the crucial assumption of Einstein's theory is not that there are no special frames, but that there are no special frames where the laws of physics are different. There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe.

    And how is the CMB "arbitrary"? It would seem to be a universal comparator.
    Last edited by Cougar; 2010-Dec-22 at 01:37 AM. Reason: Clarify that last question
    Everyone is entitled to his own opinion, but not his own facts.

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    Actually, I never disputed anything in that quote. Rather, I disputed Staticman's claims that modern views of the vacuum constitute a medium, with a rest frame in the laws, through which quantum-field-theory waves propagate. Instead, I claimed the modern view of waves has gotten away from the need to have a medium in the first place. None of that says that there is not some frames that are more convenient than others, or that spawn a more "natural" language to talk about what is happening in the universe. The British Columbia physicist is either being loose with his language, or is being misinterpreted. To say that there is "in some sense a rest frame" of the universe can easily be intepreted, and indeed should be interpreted, as simply a statement that there are some coordinates that seem a lot more natural than others. We do that in physics all the time-- do we not say that gravity points "down"? Is that a law of physics? No, it is merely a convenient language for talking about the completely arbitrary coordinate choices that give a sense of direction to gravity. So it is with the rest frame of the CMB.

    What is "arbitrary" about the CMB is that it is an artifact of history, like the clothes you are wearing right now, rather than anything that is embedded in the laws of physics as we currently understand them. If the CMB were not there, the universe would need a different history, but not different laws.

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    Well, here is Wilczek's description for lay folk:

    The model Nature gives us for making force-carrying particles heavy is superconductivity. For inside superconductors, photons become heavy! ... Photons... are moving disturbances in electric and magnetic fields. In a superconductor, electrons respond vigorously to electric and magnetic fields. The electrons' attempt to restore equilibrium is so vigorous that they exert a kind of drag on the fields' motion. Instead of moving at the usual speed of light, therefore, inside a superconductor photons move more slowly. It's as if they've acquired inertia. When you study the equations, you find that the slowed-down photons inside a superconductor obey the same equatjions of motion as would particles with real mass.

    If you happened to be a life-form whose natural habitat was the interior of a superconductor, you'd simply perceive the photon as a massive particle.

    Now let's turn the logic around. Humans are a life-form that observes, in its natural habitat, photon-like particles, the W and Z bosons, that are massive. [Earlier Wilczek pointed out "Left to themselves, according to the equations that define them, [the W and Z bosons] would be massless, like the photon and the color gluons. Reality's script, however, calls for them to be heavy.] So perhaps we humans should suspect that we live inside a superconductor. Not, of course, a superconductor in the ordinary sense, that's supergood at conducting the (electric) charge that photons care about, but rather a superconductor for the charges that W and Z bosons care about... Thus we come to suspect that the entity we call empty space is an exotic kind of superconductor.

    Where you have superconductivity, there's got to be a material that does the conducting. Our exotic superconductivity works everywhere, so the job requires a space-filling material ether.

    Big Question: What is that material, concretely? What is it that, for the cosmic superconductor, plays the role that electrons play in ordinary superconductors?
    Well, Wilczek goes on to point out that no presently known form of matter has the right properties. But he says we have a name for it: the Higgs condensate. Obviously, this is not the luminiferous ether of old....
    Everyone is entitled to his own opinion, but not his own facts.

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    In my opinion, what Wilczek is doing there (and thanks for the illuminating quotes) is providing a material analog to help us understand how particles acquire mass in the Higgs model (that the LHC is even now attempting to verify). Thus he is retracing the advancement of our understanding of waves, which is a kind of bridging between the "old style" of fundamental wave (waves in material media) to the "new style" of fundamental wave (abstract mathematical behavor reminiscent of waves in material media, without the material media). Understanding always involves bringing some abstract notion into contact with something much closer to our own experience, and that may be what he is doing here, though I admit some of his words suggest he takes the picture rather literally, or at least he favors the image that this "condensate" is a kind of material medium. His word choices that make this unclear are when he said that the "entity" of empty space is an "exotic" form of superconductor-- when is an "exotic" material exotic enough to be different from a material? At this point, I'd say we are deeply into pedagogy, rather than physical theory-- we are talking about the pictures we use to understand something, rather than the attributes of a theory we can test.

    So I'm happy to leave it that if one is inclined to want to imagine that empty space is an exotic kind of material medium, for its descriptive power, then one is welcome to do that. But one can also simply take the theory at face value, without those crutches that bring it into contact with our own experience, and just say that the vacuum incorporates fields and virtual particles that have the effect of dressing the propagation of matter with the concept of mass. No reference to any material medium is then required to propagate the waves, just that waves can propagate without a medium, but the way they propagate will be affected by virtual particles and fields. What isn't clear is if the analogy with propagation in a superconductor is figurative or literal-- in other words, if the equations are exactly the same, or if they just show reminiscent behavior. I really don't know-- if the mathematics is identical, I could count that as a strong reason to attribute propagation in a vacuum as being like propagation through a material medium, and just count superconductors as "exotic." But in a superconductor, we can identify the material, we can dissect it into its parts and talk about how they interplay-- so if the mathematics is not identical, I'd say we have a simple case of a descriptive picture of a simpler system fueling our intuition about a more complicated one.

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    The only reason Wilczek seems to have to make this "descriptive picture" as he explains it is that the mathematics of QFT, specifically of QCD and outcomes of experiments in high energy physics to check QCD, forces him to do it, what other reason could he have? The "no medium needed" view has worked pedagogically very well for years.

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    But Wilczek also realizes that we do not expect there to be any frames where the laws of physics work differently. You can bet that the physics of photon propagation inside a superconductor is different in the frame of the superconductor-- you don't have to look at some external radiation to get that, you can just watch the motion of a single photon within that superconductor. When a photon has a rest frame because it is moving at less than c (as also happens in glass, for example), you can enter a frame where the photon is effectively motionless (or more correctly, the wave that tells the photon where to go is a stationary wave). This is only possible, without violating relativity, because you see the medium, and all its charges, whizzing by at a known speed, and you can account for their effects on the photon wave function. None of our current theories attribute any direct influence between the CMB and the "Higgs condensate", there isn't even any evidence that the rest frame of the condensate, if there is one (which presumably there is not), would even be the same as the rest frame of the CMB (which is clearly observable). So I cannot see it as anything but a descriptive analogy, until there is an actual theory that suggests waves propagate in a medium that has a physically meaningful rest frame. Such a theory may one day exist-- but not this day.

    Wilczek may be straddling a line between where he is simply using a pedagogically useful analogy to help motivate one way to picture how particles acquire mass, and a personal opinion about how a future theory that describes that will work. In the mean time, it simply isn't known if the CMB rest frame has any physical significance beyond a convenient frame for analyzing spatial hyperslices of a cosmological model on the largest scales-- let us not repeat the error of those who always spoke of Maxwell's equations as being designed for an aether rest frame before any experiment actually indicated that they were!

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    Thank you guys for the great insight on the subject. I am not sure why I never heard that a Proton can go thru both slits... I have only ever heard that about light. It still doesn't make complete sense because I thought it was special to light since light has no mass. But I am reading and learning. Thanks again.

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    "Goes through both slits" is one way of thinking about it. Other interpretations are available. We don't (and probably can't) know what really happens. [Cue another long discussion on what "really happens" means ]

    The two-slit experiment has been done with "particles" as big as a fullerene molecule (C60) which is about 800 times bigger than a proton

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    Quote Originally Posted by Arcane View Post
    Thank you guys for the great insight on the subject. I am not sure why I never heard that a Proton can go thru both slits... I have only ever heard that about light. It still doesn't make complete sense because I thought it was special to light since light has no mass. But I am reading and learning. Thanks again.
    Remember going through both slits might somehow seem possible for a proton but how about a fullerene molecule (C60) which is about 800 times bigger than a proton (explained by Strange above)? The double-slit experiment has been conducted with this molecule and a wide variety of light frequencies, atomic particles, atoms, and other molecules, always with the same result. Using De Broglie's interpretation there would be no mystery at all to any of it and only one possible outcome, interpretation, or explanation (the particle goes though one slit, its waves go through both slits) no matter what the size of matter being used. I think such large molecules as fullerene would seem to be very difficult for the normal QM interpretation or justify their standard explanation or stretch credibility by proposing that this molecule somehow splits or otherwise goes through both slits at the same time. Fullerene might be the largest possible molecule that could be used for this experiment. Anything heavier may not show any measurable influence concerning the influence of the related waves.
    Last edited by forrest noble; 2010-Dec-25 at 09:13 PM.

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    Quote Originally Posted by forrest noble View Post
    I think such large molecules as fullerene would seem to be very difficult for the normal QM interpretation or justify their standard explanation or stretch credibility by proposing that this molecule somehow splits or otherwise goes through both slits at the same time. Fullerene might be the largest possible molecule that could be used for this experiment. Anything heavier may not show any measurable influence concerning the influence of the related waves.
    Why do you think that? You seem to have a slightly odd version of standard QM here. The fullerene molecule doesn't split to form a wave, it doesn't act like a particle going through one of the slits while some mysterious thing goes through both. The fullerene molecule is best described as a wave in this experiment. The system's waveform interferes with itself giving rise to the above effects. Normal QM has absolutely no problem describing a fullerene molecule (or any object) producing an interference pattern due to its interaction with two slits. It is only when you try to force explanations like the one above onto it that things seem wrong. Given a carefully enough isolated system there is no reason at all that larger molecules (a virus has been proposed) cannot display quantum behaviour.
    Last edited by Shaula; 2010-Dec-25 at 11:22 PM. Reason: Fix typo

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    Personally, the language I prefer is careful to avoid taking any stance that cannot be justified by experiment, and is not required by the theory we are using to understand said experiment. Thus, we should not say the particle goes through both slits, nor should we say the particle goes through one slit or the other but the wave goes through both. Certainly the wave goes through both, but both the experiments and the theory are agnostic about what the particle is doing "along the way." So I feel we should make no claim at all about the particle's path-- an experiment that is not set up to determine that path does not allow us to say anything about the path.

    Now, one might counter that if we do equip the experiment with the ability to detect the path, we always get only one or the other, so why should it not always be one or the other if the experiment does not have that capability? But the fact that the interference pattern at the screen is different if we equip the experiment with the ability to detect the path tells us that this is a fundamentally different setup. I think the lesson of quantum mechanics is that there is no such thing as what "actually happens" when we have not the capability to say what happens-- because what actually happens, and our capability to say what happens (in principle, not worrying about any information that we are simply not privy to), are just two different ways of saying exactly the same thing.

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    The misconception seemed to be that the particle's path was some sort of hidden variable that exists deterministically and is somehow masked by quantum fuzziness or our ability to measure things. Local hidden variables contradict experimental evidence AIUI. QM describes a wavefunction, not a particle. The concept 'particle' is something we apply to model some aspects of a wavefunction. Just like we can use 'wave' for others. But fundamentally neither are adequate descriptions and we need to go back to what the maths is telling us. Things come as wavefunctions, not particles or waves.

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    Quote Originally Posted by Shaula View Post
    Why do you think that? You seem to have a slightly odd version of standard QM here. The fullerene molecule doesn't split to form a wave, it doesn't act like a particle going through one of the slits while some mysterious thing goes through both. The fullerene molecule is best described as a wave in this experiment. The system's waveform interferes with itself giving rise to the above effects. Normal QM has absolutely no problem describing a fullerene molecule (or any object) producing an interference pattern due to its interaction with two slits. It is only when you try to force explanations like the one above onto it that things seem wrong. Given a carefully enough isolated system there is no reason at all that larger molecules (a virus has been proposed) cannot display quantum behaviour.
    I think Stange's example of Fullerene, otherwise called Bucky balls, is a good example of very serious problems with QM theory explanations in that the exact geometry of buggy balls are well known. For a Fullerene molecule to turn into a wave function just because they "know" they are going to pass through a slit surely pushes credibility of such an explanation to the absolute limit. The same thing concerning explanations for every other particle. Once it (the particle) "knows" that it's going through a slit it becomes a wave that can take up many different paths at the same time. For photons or atomic particles one might wish to consider such a possibility, but believing the Bucky balls could become a wave is a clearly fantastic example, I think, concerning some of the proposals and seemingly unrealistic explanations of QM.

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