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Duality of electrons

  1. Jul 7, 2009 #1
    Hi,

    Originally this was going to be about duality of electron but after deeper study I decided against it. This is what I understand thus far -- please feel free to correct me!

    The electron is the fundamental stuff that expresses both mass and charge. The charge of the electron is opposite to that of the proton and it is said to be "negatively charge" the latter "positively charge". When describe in terms of classical, macro, world the electron manifests itself as both particles and waves.

    It is important to realize that particle-wave duality is result of explaining a non-classical entity from a classical point of view -- maybe even way of life; it is neither particle or wave even though it expresses these attributes. Further, for computational correctness the notion of particles maybe dropped. Electrons are accurately modeled and described using wave mechanics.

    The location of electron is defined by probabilistic distribution and geometrically visioned as clouds. Its locality has highest probability in the region defined by the Bohr Radius. The shapes of these clouds are determined by electrons energy level; one can't say orbit because that implies momentum.

    The electron does not have angular velocity, obviously because this would also imply an orbiting object around a central mass and contradict the quantum model. I infer it makes no sense to wonder why electrons don't fall into nucleus since it has no angular momentum, in classical terms, to decay in the first place.

    I stop here to ask questions.

    A) Why are classical terms used to describe particles? It can be confusing. Terms such as Electron Intrinsic Angular Momentum contradict uncertainty principle; besides isn't the momentum phenomena of electron totally disconnected from classical, p = m * v? Was this rhetoric introduced to appease the the classical purists at time QM was conceived -- "don't worry classical purists the electron has has momentum like everything, but it's just a different flavor your laws are not violated"

    B) Am I correct to infer from QM that a particle is a pseudo-object because nothing, at the atomic level -- strange that atom and particle terms seems obsolete to me now, exists as a single point in space-time?

    My next step is to go into more of the math. Please don't be shy about correcting me I am trying to understand and this stuff and need all help.

    Sidebar:
    Initially, I thought nature was an ineffably schizophrenic enigma. However, upon further study I've come to the conclusion that nature is just fine; disturbingly, it seems that human perception of nature is out of whack.

    About me:
    I am neither scientist nor student; however, I've been stimulated by programs on PBS, Nova, and Science channel. So, I am endeavoring to understand a bit more about what is going on by self study and interacting on forums. I am taking weird approach though. I learn only parts of classical physics required to understand QM. I'm learning the math as I go along too. I have knowledge of algebra/trig/calculus but that is simple in comparison to what I need to know.

    I am open to suggestions on how how to educate myself on this matter too! (not into college though)
     
  2. jcsd
  3. Jul 7, 2009 #2

    malawi_glenn

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    Re: Electrons

    A) since we have a correspondence between classical mechanics and quantum mechanics, e.g. we have an Hamiltoinan function in CM and an Hamiltonian OPERATOR in QM, and we have Poisson Brackets in CM and Operator COMMUTATORS in QM etc etc

    B) A particle is a particle e.g. an electron is an electron. Yes they exists at a certain point in space time and we can do measurments. But that position is governed by the probability density function evolution. So it is only MEANINGFUL to ask what the position is after we have done a measurement of it (same holds for momentum, energy etc.)

    I mean, define "pseudo-object", never never heard that term before..
     
  4. Jul 7, 2009 #3
    Re: Electrons

    I define it to be something with characteristics of point particle, synonymous to billard ball, but in reality something different. That is far as I can go with that at the moment.
     
  5. Jul 7, 2009 #4

    malawi_glenn

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    Re: Electrons

    well a billiard ball is not a point particle, so you might want to make your definition self consistent...
     
  6. Jul 7, 2009 #5
    Re: Electrons

    Hi earamsay,

    These guys won't tell you, but you can explain all of this really clearly, in terms of the statistical behaviour of continuously existing real particles and waves. They won't tell you because they think it's really clever to use an interpretation of quantum mechanics which concerns itself only with the results of measurements. Historically this notion was invented in the late 1920s as a result of Niels Bohr overhearing a discussion in a pub about the then-fashionable philosophical notion of logical positivism ('if you don't observe it, it doesn't exist'). The philosophers these days laugh at this, but then, Bohr was never a very good philosopher.

    Try allowing 'wave-particle duality' to mean (a) electrons exist, and (b) a wave field exists (mathematically represented by the QM wave function) and the wave pushes the particles around (in accordance with the ordinary QM equations).

    The resulting theory has all the same predictions as the standard one, but is just the perfectly ordinary statistical mechanics of particles with a non-classical dynamics.

    Note that then angular momentum really does mean the angular momentum of a particle swinging around a nucleus.

    And Heisenberg's uncertainty principle has nothing to do with the real properties of a particle being 'indefinite' or 'not existing' until you look at them. In this way of seeing things, the position and momentum of a particle have a definite value at all times. The uncertainties just refer to the statistical spread you would get if you repeated the measurements of complementary variables many times (since identical state preparations just give the same wave field, not the same initial particle positions).

    It's called the pilot-wave theory, or the Bohm interpretation, or de Broglie-Bohm theory.. Look it up!

    Having said this, you probably don't want to study it now, because it isn't weird anymore. How's that for the 'Tao of Physics'?
     
  7. Jul 8, 2009 #6

    malawi_glenn

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    Re: Electrons

    We have actually many threads about Bohm interpretation (pilot wave) here, feel free to use the search function :-)
     
  8. Jul 8, 2009 #7
    Re: Electrons

    I don't mean to hijack this thread...but I will for a second. malawi, I often see posts by you similar to this one in character. Well it is true that a billiard ball is not a point particle, it is clear what the original poster is trying to say. You seem to find one deviation from perfect scientific language in people's posts and ignore the rest of the post as a result. This is unhelpful, particularly when the OP has made attempts to get his point across the best he can, and a little effort in comprehending what he has written on your part would go a long way.

    The OP is absolutely right that wave-particle duality is an inaccurate description based on thinking classically about quantum phenomena. The truth is QM is entirely consistent and no dualities have to be invoked. And electron's state is represented by a vector in hilbert space, perhaps in some particular basis, and all the information about the electron is contained in this state vector. No need to invoke wave-particle duality.
     
  9. Jul 8, 2009 #8

    malawi_glenn

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    Re: Electrons

    How do I know what the OP means by "point particle"?
     
  10. Jul 8, 2009 #9
    Re: Electrons

    I'm just saying you'd often point out poster's flaws, particularly if they don't have to proper (and sometimes quite expensive) training to get all of the science absolutely correct, rather than provide them with some of your own knowledge and inform them of the correct interpretation, etc. I'm not saying this is always the case, because looking at your post history, you clearly have spent time answering questions thoroughly. But when you say "I mean define pseudo-object, never never heard that term before" it is quite unhelpful; it seems that what he means by pseudo-object (based on his first and subsequent posts) is that quantum mechanically, particles behave in a way that is somewhat analogous to point particles in classical physics, but don't behave completely in that way.
     
  11. Jul 8, 2009 #10

    malawi_glenn

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    Re: Electrons

    I don't like to interpret, one can easily make misstakes then.
    I have heard many things during the years, and "pseudo-particle" are for instance "phonons" etc, never heard it been used to describe electrons; and same with point particle, the OP seemed to know at least some of the used notation in QM, so I just wanted to check if he knows what he is talking about.

    "Please don't be shy about correcting me I am trying to understand and this stuff and need all help."

    Thus, I was not shy at all.
     
  12. Jul 8, 2009 #11
    Re: Electrons

    Good point. Just so you know, I didn't intend to offend. Just offering my two cents.
     
  13. Jul 8, 2009 #12

    malawi_glenn

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    Re: Electrons

    And I don't mean to offend the OP either, this is just my approach sometimes - especially if they say that one should not be shy ;-)
     
  14. Jul 8, 2009 #13
    Re: Electrons

    That's not what I meant when I said 'these guys won't tell you'.

    Like you would ever mention Bohm of you own accord unless someone held a gun to your head. :smile:

    Yet you persist in trying to trying to explain basic stuff to newbies asking for 'mechanisms' or 'pictures' in terms of an interpretation which denies the possibility of such explanations , then following it up with assertions that it is 'meaningless' to ask for an explanation which isn't completely confusing.

    If you refuse to make a metaphysical commitment on principle, then you have nothing to say in answer to such questions. I don't know why you bother.
     
  15. Jul 8, 2009 #14

    malawi_glenn

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    Re: Electrons

    Clearly the OP has seen documentaries which treated QM in the Copenhangen picture and he asked questions related to it, why should I then say "no forget that crap, let us talk about Bohm-interpretation instead"....
     
  16. Jul 8, 2009 #15
    Re: Electrons

    I see nothing written by the OP that refers to the Copenhagen interpretation (there is no 'picture' by definition in Copenhagen).

    The OP asked things like why electrons are still considered to have angular momentum like classical particles even in quantum theory.

    The obvious answer to that is that, well yes, it is perfectly consistent to think of electrons having angular momentum due to their trajectories going round a nucleus even in quantum theory (Bohm). However, we normally choose to concern ourselves only with the statistics of the results of measurements and so are not allowed to address questions which require us to make a commitment as to what an electron actually is (Copenhagen).

    Restricting yourself to the latter viewpoint just confuses the hell out of anyone, particularly when you don't phrase it like I just did, but try to claim that Copenhagen is the only way of looking at the problem (other ways are 'meaningless' as you say in answer to every newbie who ever asks anything).
     
  17. Jul 8, 2009 #16

    malawi_glenn

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    Re: Electrons

    Copenhagen is the default view of almost all working physicists
     
  18. Jul 8, 2009 #17
    Re: Electrons

    No it isn't. But so what? Normally a 'default' is a pre-prepared viewpoint offered to people who can't be bothered to think about the issues for themselves. If you asked physicists who deal explicitly with quantum foundations you will find very few people prepared to defend it.

    And even if it were, then that hardly means that Copenhagen should be used to the exclusion of all other viewpoints in answering newbie questions about QM - a purpose for which it is almost uniquely ill-suited (it was designed specifically to avoid having to answer fundamental questions of 'mechanism', or what happens to systems that are not being observed).

    I note - with some amusement - that in the last poll on the subject on this board (which was quickly relegated from here to the Philosophy forum by the moderators) the Bohm interpretation actually won - at least last time I looked at it.
     
  19. Jul 8, 2009 #18

    malawi_glenn

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    Re: Electrons

    And how many participated in that poll?

    Look at the university curriculum's on QM courses, it is like 99% Copenhagen.
     
  20. Jul 8, 2009 #19
    Re: Electrons

    Precisely my point. Can you name a single student who comes away from his/her university course in a state other than 'very confused'.

    University undergraduate courses are always very slow to respond to change. But they should.
     
  21. Jul 8, 2009 #20

    malawi_glenn

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    Re: Electrons

    I was not very confused? I was not even a little confused.
     
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