Lattices and Lorentz invariance

Discussion in 'Physics & Math' started by Farsight, Oct 22, 2011.

  1. Farsight

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    3,492
    I replied here. There's ample evidence for the wave nature of matter.

    It follows, pryzk. Because when waves is all there is, there is nothing else you can use to calibrate your clock to measure wave speed. So you always measure it to be the same. See The Other meaning of Special Relativity for a detailed rationale.

    It's bog-standard SR. There's nothing wrong with it.

    Electromagnetic waves do not depend on the speed of the emitter. Photons aren't billiard-particles, we can diffract them.

    It might be worth your while reading Historical background and development. Yes, it describes time in a way that is inconvenient for relativistic theories but it's still a wave equation.

    No problem. But that doesn't mean the accelerated body isn't made up of electrons protons and neutrons. Which we can diffract. The existence of these equations doesn't make that clock calibration issue go away.

    Fine. We always measure the speed of light to be the same.

    Learn to see this point. Look closely at what you're actually measuring. Those clocks are clocking up some kind of regular motion. Quartz clocks, atomic clocks, it doesn't make a blind bit of difference. If all moving clocks slow down, then that motion slows down, not "time".

    It's a meaningless nonsensical phrase that has no basis in evidential fact.

    If you like.

    I don't have a problem with that.

    No problem.

    I didn't say internal structure, I said internal rotation. The evidence is in its magnetic moment, and things like muon spin spectroscopy along with my old favourite, the Einstein-de Haas effect.

    Noted.

    When you ask me to consider a worldline parameterised with something like proper time, I point out that this proper time parameter is provided by a local clock, which is displaying a cumulative measure of local motion. When you say measured by an observer travelling along the worldline I point out that this worldline is a static all-times representation of the observer travelling through space. For the external inertial observer who we deem to be at some fixed point in space, we draw a vertical worldine. His clock rate is different, but he isn't actually travelling along his worldline either.

    I can't. I have no issue with the \(\mathrm{d}t/\mathrm{d}\tau\). But I look very closely at the terms, and I see that they are provided by local motion through space, so this is a ratio between two rates of local motion for two observers with different macroscopic motion. I don't have a problem if we say that this motion is through space over time, but I can see nothing to support the idea of moving in time or through time.
     
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  3. przyk squishy Valued Senior Member

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    And I replied [POST=2853067]here[/POST] and you never replied to that. There is ample evidence supporting quantum physics, including the wavelike aspects of matter as described by quantum physics. The points I made [POST=2852519]here[/POST] still stand: they concern the basics of how quantum physics is defined as a theory. There is an experimental basis for each one of those differences between quantum physics and classical waves.

    Again, why should that be the case? Your response is rather mysterious given that we don't observe the speed of all waves to be the same or invariant. We only observe invariance of the speed of waves propagating at the speed of light. The quantum wavefunctions associated with massive particles (the ones that constitute matter) don't propagate at the speed of light for instance, and this is not a problem for relativity.

    I largely addressed that document [POST=2698800]here[/POST]. To recap: the author's understanding of relativity is not very good, and the only correct insights he has he doesn't seem to realise are already well known.

    There is nothing wrong with it as it is usually presented: a derivation of time dilation from the postulates of invariance of c and the principle of relativity. There is everything wrong with it if you then try to use the result as an explanation for why we measure the speed of light to be invariant, when that was one of the starting assumptions.

    That is a feature of electrodynamics, and not something that is universally true of waves. So if you use this you are bringing in the validity of electrodynamics as an additional assumption. That's fine as far as the experimental basis for electrodynamics is concerned, but electrodynamics has been known to be Lorentz symmetric since the late 19[sup]th[/sup] century. So you will again end up with a circular argument if you try to explain why physics is Lorentz symmetric, assuming the validity of a Lorentz symmetric theory to begin with.

    My point was that it is a wave equation that is not Lorentz symmetric. Which it isn't. Relativistic quantum theories can't (and don't) use that wave equation because it specifically contradicts relativity.

    And it doesn't mean it is either. That's the point: we can readily imagine a fictional universe in which true point-like particles exist, and waves don't, and everything could still be Lorentz symmetric.

    No, it is a vague phrase that has no precisely defined meaning. I can think of a number of things the phrase could plausibly mean, ranging from everything from "trivially true" to "completely meaningless". Probably by time "flowing", most people are simply referring to the so-called "psychological arrow" of time, or perhaps the perception that as they get older, they see the world evolve around them.

    Same point: these experiments show that the electron and muon have the internal degree of freedom we call "spin", and that spin contributes to total angular momentum. They do not show that anything in the electron or muon is literally rotating, or that the electron or muon even have anything that can rotate (internal rotation requires an internal structure that can rotate).

    Again, how are you defining "motion" here in the first place?
     
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  5. OnlyMe Valued Senior Member

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    Przyk, if I understand you here, you are saying that an electron's "spin" is a charge like aspect and not "spin" associated with angular momentum.

    This does not seem reasonable since an electron does have a magnetic moment, which is associated with angular momentum or spin. It would be the classical spin of an electron's charge that gives it a magnetic moment.

    I have heard this issue involving spin, argued both ways. It has always seemed to me that the charge like spin was an artifact of the mathematics and the angular momentum "spin" a product of classical application.
     
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  7. Farsight

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    I replied to that post, pryzk. I said something about superposition and wikipedia, about pointlike interaction as opposed to pointlike particles, I said I wasn't keen on p=mv, I said let's look for a classical analogue, I asked you details of your Einstein 1935 reference, and said I based my interpretation on scientific evidence rather than pop science. You say the wavelike aspects of matter are described by quantum physics, I say the wave nature of matter is demonstrated by experiment, let's not argue about the fine distinction, let's move on.

    It isn't mysterious, it's just so simple that you're failing to appreciate it.

    Those are the waves that count. We aren't interested in sound waves here.

    Matter can't move at c if it consists of waves moving in a closed path at c.

    I've re-read your post, and I think you absolutely failed to address the paper. You made light of it, and found reasons to dismiss the message it delivers.

    The postulate came from the Michelson-Morley experiment, the explanation comes from Pythagoras' theorem, and there's nothing wrong in using the simple derivation of time dilation to explain why we measure the speed of light to be invariant. It involves a parallel-mirror clock, but we could equally use a mechanical clock, a quartz clock, an atomic clock employing microwaves, or an "optical" clock where ultraviolet frequencies are involved. They all rely on the rate of electromagnetic propagation, as do our thoughts and bodily processes.

    No. We don't need to know anything about electrodynamics. All we need to know is that we always measure the speed of light to be the same and that our particles have an electromagnetic nature and a wave nature.

    Noted.

    That universe wouldn't match experimental evidence. It would be science fiction, like time travel.

    The phrase time flowing at different rates isn't vague, pryzk, it's a figure of speech at best or cargo-cult nonsense at worst. Time doesn't flow. Can you offer any experiment that demonstrates time flowing? Can you open up the back of a clock and show me the proper time streaming through it like a torrent? No.

    They demonstrate that spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics.. It isn't some structure rotating as per a propellor blade, the structure is there, the electron is there because of the rotation, as per a vortex.

    As a gradual change in position. As that thing I can see happening. We say this motion occurs at some rate, but our basis for that rate is set from the motion of light, so the rate is a ratio.
     
  8. Farsight

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    3,492
    I'd venture to suggest that the "charge-like spin" is an artefact of point-particle/billiard ball concepts rather than mathematics: there are wave equations for the electron. But despite this and despite the fact that we can make an electron out of an electromagnetic wave in pair production, and despite the fact that we can diffract an electron and demonstrate its magnetic moment, contemporary physics doesn't seem to allow for a wave in a tight closed path.
     
  9. przyk squishy Valued Senior Member

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    Where did you say all this?

    By the way, the 1935 reference in question is the paper that introduced the now famous "EPR paradox", pointing out the nonlocal nature of entangled multiparticle states in quantum physics. You can get a copy of it here.

    What? The wavelike aspects of matter specifically as described by quantum physics are extremely well supported experimentally. That does not give you carte blanche to wave away the details and say anything you like about everything being made from waves.

    I was specifically talking about the quantum mechanical wavefunctions. Their phase and group velocities are not c. And I have never heard of any model in which fundamental particles are modeled as "waves moving in a closed path" that actually works.

    I think this absolutely fails to address my post. Many of the issues I had with that paper are the same as the ones I'm having with you now (which is hardly surprising since that paper is where you seem to have gotten many of the ideas you're posting). Merely pointing to someone who says the same things you do does not strengthen your case, unless that person makes a stronger case than you do. And Robert Close doesn't make a good case for his position, for the reasons I've explained.

    It doesn't matter where it comes from. The issue here is that using an argument that uses invariance of c as a postulate to explain invariance of c is circular.

    No, the explanation comes from basic geometry and kinematics, invariance of c, and the principle of relativity (that the laws of physics are the same in all reference frames).

    Not exactly. First, you need time dilation, length contraction, and the relativity of simultaneity effect to explain invariance of c. Time dilation alone isn't enough.

    Second, no-one has ever shown that you can explain all these effects for arbitrary physical systems based on "the rate of electromagnetic propagation". People like Lorentz, FitzGerald, Larmor, and Poincaré did however argue for these effects in the late 1880s and 1890s based on the increasing awareness (at the time) that matter was held together by forces that were electromagnetic in origin, but they were appealing to the whole of electrodynamics and not just the propagation of electromagnetic waves.

    Third, this misses my point, which is that it is circular to "explain" invariance of c and/or Lorentz symmetry using results that were derived using the invariance of c and/or the validity of electrodynamics (which is Lorentz symmetric) to begin with. Especially when you get the "explanation" wrong: the way light propagates alone does not imply that all clocks will dilate just like the parallel mirror light clock does. But the fact that all clocks are governed by electrodynamics and other Lorentz symmetric laws does imply this. Exactly why any given clock dilates when in motion will depend on details about how that particular clock works, but applying Lorentz symmetry we always know what the end result is going to be.

    It would also be a proof of principle. If I can theoretically describe a universe that is Lorentz symmetric and yet does not contain waves, I have demonstrated that waves are not logically required in order for physics to be Lorentz invariant. We've known how to very easily put together Lorentz symmetric theories since Minkowski's work on the subject. It doesn't automatically require waves.

    Just what exactly is your issue with time travel? I could understand you pointing out that there is no evidence such a thing as time travel is possible. I could understand you pointing out that current theory either doesn't seem to allow for it or at best suggests it is unlikely to be realisable in practice (given GR does predict the possibility of closed timelike loops after all). I could understand you pointing out that the idea seems problematic because of arguments like the grandfather paradox. But dismissing the idea as science fiction, as if you wanted to put a taboo on it? Given that we're still a long way from understanding everything there is to understand about our universe, that's just plain narrow minded.

    Can you show me a single person saying that time does flow, and that what you've said above is actually an accurate summary of what they mean by that? Can you show me a single person expressing the belief that if you did open the back of a clock, you would see "proper time streaming through it like a torrent"?

    In the sense that spin is a form of angular momentum and contributes to the total angular momentum of a system. Nothing else is demonstrated. No experiment demonstrates that anything is really rotating, in any sense of the word, in the electron or muon.

    Evidence...?

    Change in position over what? Time? This is the key point here: in general it doesn't mean much just to talk about some quantity or parameter changing. Parameters change with respect to other parameters.
     
  10. Farsight

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    3,492
    In a post that I can't find. Sorry.

    Thanks.

    What else are they made from then? Something that surpasseth all human understanding?

    New models tend to struggle to get attention. See this page on spherical harmonics. See the bit that says They are used to describe the wave function of the electron in a hydrogen atom? The electron wavefunction here isn't moving in some linear fashion, it's in a closed path, moving at circa 1/137th c in harmony with the proton wavefunction. Apply the same kind of thinking to pair production.

    My previous comment stands.

    That's not what I'm saying. I'm saying that when you're made of waves, you always measure wave speed to be the same. Because you use wave speed to calibrate your rulers and clocks, which you then use to measure wave speed. So regardless of how fast light moves, you always measure it to be 299,792,458 m/s. Have you forgotten what I told you about the optical clocks losing synchronisation at different elevations? And how you can simplify them to parallel-mirror light clocks? I'm not using the invariance of c here.

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    I rather fear this is becoming a circular argument between us pryzk.

    Those things aren't enough. Because they don't come first.

    I've been trying to keep things simple.

    Sigh. We've already been through this. The postulate emerged from the MM observation of the invariance of c.

    You can take any clock and separate it into electrons, protons and neutrons. Wait a while and the neutrons decay into electrons protons, and antineutrinos which depart at c (or thereabouts). Then you can add positrons and antiprotons and annihilate everything down to gamma photons, which depart at c. That's why those "laws" hold true.

    Yes we do. And we should also know why Lorentz symmetry holds, at a deep fundamental level, not just because it's some law of physics.

    It would be science fiction, pryzk. Not proof of principle.

    It's science fiction. No, let me rephrase that: it's cargo-cult pseudoscience woo trotted out by celebrities who pretend to be promoting physics but are in truth promoting themselves. Neutrinos travelling faster than light? Hey! Time travel!

    Not when you look at what clocks do. Then you see that time is a cumulative measure of local motion, and there is no forward "travel through time". And no negative motion either. So backward time travel is totally out. I'll continue with this reply later.
     
  11. przyk squishy Valued Senior Member

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    Er, I don't have to tell you what something is to be able to tell you what it is not. In science, no explanation is always hands down better than a bad, wrong, or unsupported explanation.

    New models can also be wrong or inadequately supported by their proponents.

    So what's your reasoning here? That because the quantum model of the hydrogen involves spherical harmonics, it is "obvious" that the electron can be modeled as some bound wave state? It isn't obvious, and it is up to you to support the idea, in particular showing that you can do it in a way that doesn't break the ability of mainstream theories of the electron to account for the countless thousands of experimental results they very successfully do.

    No, the comments I made in my old post still stand, given that you haven't addressed any of them.

    But you haven't supported any of this, and it is becoming increasingly apparent that you have no idea what supporting an idea even means in physics.

    And we don't normally use "wave speed" to calibrate rulers and clocks. At the time of the Michelson-Morley experiment, I think the metre was just defined as the length of a standard bar kept in France, and the second was defined as 1/86400 of a day and in practice measured using pendulum clocks. The silly thing is, a number of people, even before Einstein's original 1905 publication, did a much better job of explaining why moving clocks would time dilate and measures of distance would length contract than anything you or Robert Close have been able to offer.

    Since you have not presented any of your own derivations for anything you are asserting, it is not clear to me at all what you are using. All I've got to go on is that you cited the derivation of time dilation based on the parallel mirror light clock, and that does use invariance of c as a postulate. So if you want to give an explanation that isn't circular of why we measure the speed of light to be invariant, you can't use that derivation. Since you haven't presented anything else either, you're on your own at this stage.

    No, they're enough. I can readily show you that if all measuring devices experience length contraction, time dilation, and relativity of simultaneity effects, we will always measure an invariant c using them. It isn't much fun to do this, mind you, but it's the sort of thing I did as an exercise when learning relativity several years ago, and I can post a proof if it really becomes necessary. I can also show that relativistic time dilation, on its own, does not get you an invariant c.

    No, because we use clocks that haven't been broken down into their constituent elements and haven't been bombarded with positrons or antiprotons, you haven't explained anything.

    Well if you can give a real, valid explanation for why the laws of physics are all Lorentz symmetric, then by all means do so. But keep two points in mind: I'd rather have no explanation than a bad one, and it is a logical inevitability that there will be fundamental things we can't explain, so you can't reflexively demand explanations for everything and expect answers.

    No, it is a proof of the point I was making, and dismissing it as "science fiction" just looks like name calling to me. You are still confusing the difference between the universe happening to be a certain way, and it being logically necessary for it to be a certain way. Whether the universe happens to be Lorentz symmetric and/or partially or completely "made of waves", and whether it is logically possible for a universe to be Lorentz symmetric and yet contain no waves, are two different things. A toy model can readily prove the latter point.

    Are you attacking the idea of time travel here, or the people you see publicly advocating it?

    What, just simplistically look at clocks, with my biased brain that is naturally predisposed to looking at space and time in completely different ways? I don't think that's a good idea.
     
    Last edited: Nov 21, 2011
  12. Farsight

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    Reply continued from previous post:

    Yes, Stephen Hawking, see this article and note the quotes.

    I think so. Read that article. "Time flows at different rates".

    No. But there's plenty of people who insist that clocks measure proper time.

    Come off it pryzk. Magnetic moment is real. Spherical harmonics isn't some quack theory. A real life experiment like Einstein-de Haas demonstrates that spin angular momentum is of the same nature as ordinary angular momentum. And Stern-Gerlach demonstrates spin. But what? There's nothing really rotating because that would mean some billiard-ball would have to rotating faster than c? I'm sorry, but that's pink-elephant logic. And it totally misses why AND relates to multiplication.

    Gravitomagnetism. Go search on that and vortex. And note that it isn't called gravitomagnetism for nothing. Then look at the original Maxwell.

    Change in position over time, which is derived from the change of position of light. So it's change of position over change of position. That's why I said the rate is a ratio. Come on pryzk, a child can understand all this. Why can't you?
     
  13. Reiku Banned Banned

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    11,238
    Really?

    I don't think that is very accurate. There are many experiments which rely on the fact matter behaves like waves at the fundamental level.

    The first and foremost is the Double Slit Experiment. How do you reconcile that experiment without a wave property of matter and energy?
     
  14. Farsight

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    pryzk: I've read your latest post. I don't think we're getting anywhere here, and I think we should call it a day. It's been interesting and informative talking to you.
     
  15. AlphaNumeric Fully ionized Registered Senior Member

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    I'll just pick one thing to look at from your posts....

    You're showing you don't understand what pryzk said.

    He was commenting about how 'spin' in quantum systems doesn't necessarily mean something is literally spinning, they just have the same commutation relations are classical angular momentum.

    And what is it with you and spherical harmonics? Saying "It isn't actually spinning" is nothing like "There's no spherical harmonics!". The wave function of the electron in the Hydrogen atom includes spherical harmonics, it's one of the most basic and well known analytic solutions in all of quantum mechanics. But at the same time the extension to include the additional parameters to generalise to a Hydrogen atom in a magnetic field doesn't mean something is literally spinning.

    You clearly don't understand how all of this hangs together in the eyes of the mainstream physics community, especially in areas involving mathematical physics. You showed that when you asked me to do some vector calculus only related to electromagnetism, as if there's a 'physicists mathematics' which you could separate off. And to top it off you don't have any really experience with any experimental set ups, either doing the experiments or modelling them, yet you presume to tell people who do. Said people might not be exactly right but you have less information, less experience and less competency in every single thing related to the matter at hand so why do you presume to tell others how things are?

    I know you've thought and thought about this stuff, having read a pop science book or two but Jesus, give it a rest. At some point you're going to have to accept you've failed to come up with anything viable. These discussions always end up the same way, someone like pryzk walking you through mistake after mistake, both practical and theoretical, you have and you basically waving it off with the attitude "Well I know how it actually works and you lot just don't want to be taught!".

    If it weren't for the fact pryzk makes very good posts there'd be little to keep your posts out of pseudo or the cesspool. Your contribution to the forum seems to be initiating so many corrections from others that you set yourself up as an example of how not to be.
     
  16. przyk squishy Valued Senior Member

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    True, he says that, but from context I think he's more interested in the idea that you could quickly visit the future by sitting in the right place than he is in the idea of formulating a theory about time literally "flowing". Even physicists use similes and metaphors sometimes.

    And they do. Almost by definition.

    Did I ever say otherwise?

    They are also not involved in modeling spin. They certainly can't explain spin half particles: spherical harmonics are a family of functions, often noted \(Y_{l}^{m}\). In quantum physics they are orbital angular momentum eigenstates, with the integer index l referring to the total angular momentum, and the integer index m, ranging from -l to l, referring to the projection of the angular momentum along a given axis. The spherical harmonics corresponding to half integer values of l don't exist. There are no such spherical harmonics. In the framework of quantum physics it is fundamentally impossible to explain half integer spins in terms of orbital angular momentum.

    No, that's just what the Wikipedia article says. And it's right only in the specific sense I explained earlier: spin contributes to the total angular momentum of a system and participates in the total angular momentum conservation law (i.e. you can trade spin for orbital angular momentum). The experiment does not demonstrate that spin is orbital angular momentum.

    Incidentally, I find the statement that "This is remarkable, since electron spin, being quantized, cannot be described within the framework of classical mechanics" in the Wikipedia article a bit odd, since orbital angular momentum is also quantised in quantum physics, and we generally recover classical mechanics on average from quantum mechanics. A single spin or particle with a certain orbital angular momentum doesn't look very familiar, but it is not especially surprising that the total angular momentum of a large quantum system can start to look like classical angular momentum.

    No, a simple statement of fact: it is incorrect to say that the Einstein-de Haas effect shows that spin is really orbital angular momentum. The experiment only shows that spin appears in the same conservation law as orbital angular momentum: if you forcibly change all the spins in a system, the spin "deficit" goes into its orbital angular momentum.

    Once you have established that fact, you can then try to come up with hypotheses to try to explain that fact. At first, a very natural approach might seem to be to explain the observation with the hypothesis that spin is actually just fundamentally implemented as orbital angular momentum. The Einstein-de Haas effect does not directly show this, but it is a very natural explanation one might think of for it. But unfortunately it doesn't work: as I explained above, we know spin half particles exist, and quantum physics is fundamentally incapable of explaining half integer spins in terms of orbital angular momentum.

    Is this what you call supporting your case? How is any of this evidence that "It [presumably the electron] isn't some structure rotating as per a propellor blade, the structure is there, the electron is there because of the rotation, as per a vortex."?

    But there are many things that are problematic with this idea. First, where is this idea that you can express the position of something in terms of the position of something else coming from? How do you make the comparison? What's the difference between two objects being in the same place at the same time, and being in the same place at different times? I think you've still got an assumption of the notion of simultaneity buried in there somewhere. Second, you can't always do this consistently, as the relationship between the positions of two objects is not necessarily bijective. Third, how do you reformulate general relativity, which explicitly models time as part of a spacetime manifold, in these terms? When you start looking at issues like these, the idea quickly starts to look like it'd be more trouble than it is worth.

    You know the simplicity and the validity of an idea are two different things, right? :bugeye:
     
  17. przyk squishy Valued Senior Member

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    My point was that it is inaccurate to characterise quantum physics as saying "everything is made of waves". Sure, particles have "wavefunctions" and exhibit wavelike behaviour in some circumstances, but that is by no means all there is to quantum physics.
     
  18. Reiku Banned Banned

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    ok.
     
  19. przyk squishy Valued Senior Member

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    Just a point for Farsight, because it does get annoying to be lectured on stuff you already know about from someone who doesn't:
    Farsight, that means that you can expect everyone who studied physics in university to know about spherical harmonics and something about how they're used in physics. On this forum, that includes AlphaNumeric, prometheus, CptBork, James R, D H, and I, and no doubt many other posters who visit here less frequently. So when you find that we don't share the same sentiments about spherical harmonics as you do, it is not because we are ignorant of them.

    Same general comment regarding pair production, the electromagnetic and electromagnetic potential fields, the Aharonov-Bohm effect, the Stern-Gerlach experiment, quantum field theory, ...
     
  20. Farsight

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    Noted pryzk. I have to say though that some of the things you and prometheus have said on this thread have surprised me. It's as if you're too close to your subject, and find it difficult to step away from the mathematics to consider the evidence and examine the concepts you currently hold. I know I said I think we should call it a day now, but I'll do you the honour of responding to your post above.

    There's other material from Hawking concerning time. Such as the Chronology Protection Conjecture. I'm afraid I have a very low opinion of this sort of thing.

    But they don't. They all operate by accumulating some kind of regular motion. That's all they do. That's what you can see that they do.

    No you didn't. But you did say Nothing else is demonstrated. No experiment demonstrates that anything is really rotating, in any sense of the word, in the electron or muon. Magnetic moment challenges this.

    Did you spot me saying quasi spherical harmonics at some point? Take a look at http://www.bpreid.com/poas.php and think of an equatorial rotation at c and a simultaneous rotation towards the North pole at ½c. It's a toroidal harmonic.

    I didn't say it does. I said the Einstein-de Haas effect demonstatrates that spin angular momentum is of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics. I might claim that intrinsic spin is a special-case subset of orbital angular momentum, wherein a wave is in a tight close "orbital" around and through itself, but saying spin is orbital angular momentum doesn't sound right. Thats sounds like claiming that the rotating earth is orbiting.

    Fair enough.

    Read this "history" version of the wiki Stern Gerlach experiment:

    "Electrons are spin-1⁄2 particles. These have only two possible spin angular momentum values, called spin-up and spin-down. The exact value in the z direction is +ħ/2 or −ħ/2. If this value arises as a result of the particles rotating the way a planet rotates, then the individual particles would have to be spinning impossibly fast. Even if the electron radius were as large as 14 nm (classical electron radius) then it would have to be rotating at 2.3×1011 m/s. The speed of rotation would be in excess of the speed of light, 2.998×10^8 m/s, and is thus impossible.[2] Thus, the spin angular momentum has nothing to do with rotation and is a purely quantum mechanical phenomenon. That is why it is sometimes known as the "intrinsic angular momentum."

    I think this is wrong.

    See above.

    Conservation of angular momentum means its a real rotation.

    Give it time pryzk.

    I'm just trying to explain it to you.

    Everything gets very simple, really.

    Yep. Don't forget I'm backing up my argument with references to experiment.
     
  21. rpenner Fully Wired Valued Senior Member

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    There are three weird bits about electron spin, the magnetic moment is too high to be explained in terms of a rotating charge distribution tied to a rotating mass distribution, the angular momentum is very large compared to the experimental size of the electron, and the spin obeys quantum and not classical rules which precludes whole classes of mechanical models.

    The approximate value of the ratio between magnetic moment and intrinsic angular momentum was an early success of Dirac's model of the electron as a point-like particle in a Poincaré-invariant quantum field theory which was developed into Quantum Electrodynamics (QED) which treats the electron field as coupled to the photon field. QED's prediction of the precise value of the ratio between magnetic moment and intrinsic angular momentum is often touted as one of the most precise agreements between theory and experiment. I believe it was Eugene Wigner who demonstrated (in 1939!) for a massive particle Poincaré-invariance (in 3+1 dimensions) admits arbitrary unitary representations corresponding to SU(2) which "explains" why we have quantum field theories corresponding to spin-0, spin-1/2, spin-1, etc particles.

    http://www.jstor.org/pss/1968551

    So all three problems are well-addressed by the hypothesis that the electron is well-modeled by a Poincaré-invariant quantum field theory of a finite mass spin-1/2 particle coupled to the massless helicity-1 field of photons. There's a lot of heavy lifting to get from that to numerical comparison of experiment with theory, but it's a simple hypothesis that is far more precise (and useful) than "matter is made of waves."

    That historic page is almost 2 years old, but does not date the paragraph in question, which is older. The paragraph is present in the present version with the main difference apparently being the correct value of the classic electron radius which I remember approximately as 53 pm / 137^2 = 2.8 fm.
    Further, footnote 2 points to the source as the Pop Physics book The Story of Spin (1997) which has been dumbed down for a general audience.

    The basic sentiment was added to Wikipedia in May 2006.
    http://en.wikipedia.org/w/index.php?title=Stern–Gerlach_experiment&oldid=53227603
    Later versions would drop the LaTeX. The reference to the speed of light argument and the pop science book were added in October 2007. http://en.wikipedia.org/w/index.php?title=Stern–Gerlach_experiment&oldid=164001483

    But if you want to critique the calculation, it is the pop physics book you need to attack, not the stale link to Wikipedia.


    That's not a reason for anyone to think this is wrong. Are you a cult leader? Are you talking to six-year-olds? No? Then you need to do better than a naked statement of your instant opinion. Why do you think this is wrong? Is there a factual basis or just some intuition? If intuition, when has that ever worked out well for you?
     
  22. Magneto_1 Super Principia Registered Senior Member

    Messages:
    295
    Farsight, here I agree with you. When I studied this experiment, and Stern Gerlach, I discovered, that this guy Otto Stern, did not want a classical interpretion of a spinning electron like a spinning top. Because he worked for Max Born, who also wanted QM to be mysterious.

    From my study, I sense that this guy Otto Stern, wanted Quantum Mechanics to remain wierd.

    But in fact it seems that all masses, planets, stars, and galaxies spin in the classical sense.
     
  23. Tach Banned Banned

    Messages:
    5,265
    LOL, you two should combine forces and start a TV program. Could be titled "Physics: The Fringe Zone". It would be a sure hit on the SciFi Channel. Or is it the Comedy Central Channel? Maybe both.
     

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