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Wave-Particle Duality

  1. Apr 21, 2005 #1
    This is my understanding towards wave particle duality:
    Matter is neither wave or particle.The matter position can only be determined when we observed the matter. When the matter is not observed, the matter can be in any position, and have a wave function.
    So, I make the following deduction:
    When an electron is not observed, it behaves like a wave. The electron will "replicate" itself into infinity amount of "abstract" electron. I call them abstract, because they will not interact. Thus, when the electron is observed, one of the "abstract" electron become "concrete" electron.
    Is the deduction true?
    Feel free to criticized, correct or advise. :smile:
  2. jcsd
  3. Apr 21, 2005 #2
    One more hidden variable lover :wink: .
    If you really want to explain coherently the results of QM measurements with hidden variables, please look at the bohmian theory of QM (there's a lot of good papers on arxiv). This is actually the most coherent adpatation of QM theory using hidden variables.

  4. Apr 21, 2005 #3


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    seratend, I see no reason why scilover89's attempt to understand duality should cause him/her to be shunted into Bohmian mechanics. Better to come to some understanding of what standard QM says and then look into whether Bohm seems attractive than wind up with a distorted view of what's what.

    scilover, saying the particle is a wave when it's not observed is partly right and partly wrong. The particle when it's not observed is represented by an Amplitude wave (also called an amplitude, a wave-function, a state-function, or just a state). This is a mathematical wave expressed in complex numbers, and it takes its values in an abstract "Hilbert Space" not in our spacetime world. It might be expressed in terms of subtle features of our world, that's what seratend means by hidden variables, but it's important to know that most professional quantum physicists don't think that is so.

    When we observe, the wave function is projected into our world, but it appears here not as an existence but as a mere probabilty. So what you get is mathematically well-defined but in terms of existence rather loose. Either a wave or a particle, depending entirely on what kind of observation you did.
  5. Apr 21, 2005 #4
    When a particle is not being observed it cannot be said what it is. In fact we can never say what a particle is. All we can say is how its behaving and when can only say that when its being observed.

  6. Apr 21, 2005 #5
    Well, [one of] the main problem of QM interpretations (especially the wave particle duality) relies on whether the values given by an observable "exist" with or without a measurement (e.g. does a particle has a path?, i.e. does it always have a [implicitely hidden] defined position).

    [To the users of PF, by measurement result, I just mean, a logical proposition such as "particle is at position x" is true. Nothing more (the rest is mainly interpretation).]

    QM postulates do not require the existence of such a property when there is no measurement [result]. Only the "lovers" (in a non-pejorative sense) of hidden variables implicitly assume this.
    The post of silcover in many sentences assumes the existence of properties without measurement:
    The electron will "replicate" itself into infinity amount of "abstract" electron, I call them abstract, because they will not interact. Thus, when the electron is observed, one of the "abstract" electron become "concrete" electron.

    This is mainly the bohmian view of particles. He is assuming the existence of a hidden path (the preexistence of the abstract independant electrons) => He is implicitly a lover of Hidden variable theories.
    Therefore, I recommend someone who needs a hidden variable ground to understand better QM results to check Bohmian mechanics. In my modest opinion Bohmian mechanics is an excellent coherent model for QM HV (there has been a lot of developments to correct the incoherencies of this model).
    Having another way to view the results of QM may help one in understanding the standard QM (removing the many confusing interpretations). In other words, by changing some of the words used by standard QM, Bohmian mechanics may help one to understand what the QM words (“measurement”, “collapse”, etc ...) do not say (the implicit assumptions).

  7. Apr 21, 2005 #6

    I hope you don't find this post condescending; I do not (and would never) mean to imply that, but can understand that it could be interpreted that way.

    You must understand that the world isn't classical; but classical logic is what your brain understands well, because that is what it has grown up experiencing. But to truly be at home with the world, you must realise it is quantum.

    Don't make deductions such as "when the electron is not observed it is a wave" -- look at the postulates of quantum mechanics. What do they have to say? Are you even sure what you mean by "when the electron is not observed"?

    A lot of people come onto these forums, and the main reason they have problems understanding QM is because of their unfamiliarity with the postulates of QM. I think it's great that so many people want to understand physics, but they must realise that the great power of QM lies in the power of it's mathematical framework.

    Reading popular science books will tell you all about systems behaving sometimes as waves and sometimes as particles. This is wrong -- they always behave in a quantum way, which is neither a wave nor a particle. If you want more information, look up the mathematical formulation of QM on the web; look up terms you do not understand; many books have been recommended on this forum for people who want to learn, if you search you will find a very comprehensive list.

    I hope this helps.
  8. Apr 23, 2005 #7
  9. Apr 23, 2005 #8
    Please, precise what you intend by "observed". This word is most of the time the source of many wrong claims in QM.

  10. Apr 24, 2005 #9


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    There are many errors: what an electron is, it doesn't matter. The core of the problem is in the kind of measure you realise: a momentum or a position measure? You would observe respectively wave (like interference, double slits) or particle (precise position) behaviour. This is what we can say.
    An electron has no position neither momentum, unless it is not observed (reality, Bell...). The eigenvalues of |Psi> allow only to calculate the expectation value.
  11. Apr 24, 2005 #10
  12. Apr 25, 2005 #11


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    If two variables don't respect the commutation parenthesis (i.e. [A,B] =/ 0) you can have complete non localized A and completely localized B, it respect the indetermination pronciple. You can have an experimental proof if you think to a pulsed laser: the shorter is the pulse, the wider will be the chromatic bandwidth, just because to have a delta function on the time variable, you need a superposition o many waves with different frequencies (at the limit, transform limited). This means you have for example localized in time your photon, but don't know it's colour. The same happens with position and momentum.
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