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De Broglie's wave frequencies for particles

  1. Sep 17, 2010 #1
    I was reading today about de Broglie and I don't think I really get what is meant by particles having a wave frequency. What is being measured as a wave, the oscillation of the electrons? Also, the book said something about the electrons sending out waves that move faster and even catch up with it after a complete orbit. Does this mean that EM energy is being constantly sent out by electrons and the photons orbit around the nucleus as well, feeding back into the electrons?

    btw, sorry I don't remember the title or author of the book I was reading to post it.
  2. jcsd
  3. Sep 17, 2010 #2
    In quantum mechanics things on the atomic scale have both a particle nature and a wave-like nature. The de Broglie equation gives, in literal terms, the wavelength of a particle of mass m and speed u.
  4. Sep 18, 2010 #3
    So what is it that is oscillating as waves with variable wavelength? The electrons? The EM energy generated by the electrons?
  5. Sep 18, 2010 #4
    The oscillating variable is psi, called the wavefunction of the particle. psi squared is the probability of the particle being in a given state (of having a certain momentum, of being at a specific location, etc.)

    Welcome to QM.
  6. Sep 18, 2010 #5
    So it doesn't refer to the features of a hypothetical object but to a probability function for where something could be located? It doesn't describe anything about the mechanics of how the thing functions, just how to predict the position of components?
  7. Sep 18, 2010 #6


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    All we know for sure is that the psi function allows us to calculate probabilities of obtaining the various possible values for experimentally-measured quantities. Beyond that, we are in the realm of interpretations of QM, of which there are several viable ones (i.e. ones that agree with experiment). Discussions and debates about QM interpretations are common here, but they seem to have died down for now, probably only temporarily.
  8. Sep 18, 2010 #7
    Thank you for clarifying this for me. It sounds like what you are saying is that QM begins with measurement data and develops mathematical expression that describe and predict the data. Then people attempt to interpret what the patterns mean and what causes them. It sounds a lot like statistical sociology.

    Could you explain the apparatus that generates experimental measurements? Does it send some kind of impulse into a substance and record the impulse returned? Is the impulse electricity or radiation? Are there many atoms or few involved? Is it that they try to create a relative vacuum and make it very cold to slow down the atom as much as possible? What is then measured? What is interpreted/measured to represent the position of an electron?
  9. Sep 18, 2010 #8
    It refers to its features (the set of which is called its state), but the features (state) cannot be determined in an absolute fashion, only probabilistically, through psi^2. QM is the mechanics of psi, which is related to physical "things", through the probability psi^2.

    Einstein didn't like the idea of probability in mechanics, but he (or anyone else) has not been able to find anything deterministic (such as newtonian mechanics). Experimentally, QM theory is the only one that fits the data of small scale phenomena. And it does so flawlessly in this respect.

    It is arguable that on the small scale, since phenomena is not deterministically observable (it is experimentally impossible to follow the path of an electron around a nucleus, because an observing photon would change the electron's original course), a deterministic theory doesn't make any sense. In physics, a successful theory is one that fits experiment.

    Theories that can't be matched to experimental data can be clever, beautiful, elegant, but they remain theoretical until proven by experiment. String theory has all this except the experimental part. Classical mechanics has all that, plus some experimental success. QM has everything, including constant experimental success.
  10. Sep 18, 2010 #9
    That may be how it was developed in the beginning. But now, one can use the theory and predict new data successfully.

    Too many to mention. The entire periodic table, spectroscopy, lasers, superconductivity, crystal behavior, nuclear physics, classical mechanics, electrodynamics, much of astrophysics, can all be explained with QM's few basic equations (basically Shrodinger's eqn, its variants and its consequences, such as HUP.) There are a few historical, key experiments though (such as the double slit exp., the Stern-Gerlach exp., radioactivity etc.).
  11. Sep 18, 2010 #10
    What I want to understand is the specific workings of a particular piece of instrumentation for measuring electron position. I would like to try to critically analyze the functioning of the instrument itself to see what, if any, measurement effects on the data there might be - or if something else could be getting measured other than the presumed phenomenon.
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