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Bhor's rule breaking energy levels

  1. Jan 24, 2010 #1
    Bhor's rule breaking "energy levels"

    when Ernest Rutherford's model of planetary system to explain the atomic structure, he was forced to have the regret by the fact that "accelerated charges dissipate their Kinetic energy into EM radiations."
    Bhor tried to avoid it.So he engaged the idea of "energy levels" in order to avoid the maxwell's discovery. Just by propounding that the electrons around the nucleus revolve in "energy levels" ; how can electrons get license of not losing their energy while moving in those "energy levels"?
    how did he convinced the people?
  2. jcsd
  3. Jan 24, 2010 #2


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    Re: Bhor's rule breaking "energy levels"

    His theory agreed with experimental data.
    That is really all you need in order to convince people you are right.
  4. Jan 24, 2010 #3
    Re: Bhor's rule breaking "energy levels"

    That is a cliche which people keep repeating with regard to quantum mechanics and I don't believe it has ever been true. People use it precisely as an excuse to permit themselves to accept something even though they haven't been convinced. It has become a mantra of physics because most of the time we don't understand what we are doing, and we need an excuse to justify proceding on that basis.

    The problem with Bohr's theory was that it didn't MAKE SENSE, even though it agreed with certain experimental data. And soon enough it was discarded, to be replaced by a theory that actually made more sense. And that's what you really need to convince people: something that not only agrees with the data but actually makes sense.
  5. Jan 24, 2010 #4
    Re: Bhor's rule breaking "energy levels"

    The presence of energy levels solves two things.

    1) It implies the presence of a lowest energy state, which is therefore a stable state. The electron cannot decay into a lower energy state, so you end up with a stable configuration. This solves the problem of accelerating charges which constantly radiate energy, and must end up at the atom core.

    2) Electrons which hop from a higher state to a lower state radiate a photon with a very specific wavelength. Therefore the emission spectrum of an atom is discrete, with the wavelengths corresponding to differences in energy between the energy levels.

    Ofcourse the Bohr model is hardly able to justify the existence of these energy levels. You need quantum theory for that. But the fact that the discrete energy levels qualitively solves some of the problems of the 'classical model' is a great accomplishment.
  6. Jan 24, 2010 #5
    Re: Bhor's rule breaking "energy levels"

    The Bohr's model main problem is not the EM radiation of the "accelerated charges".
    His theory explained that the electron is stable when the orbital length is a integer times the de Broglie's wavelength.
    (Sorry. to be precise, the Bohr's original theory is the quantization of the angular momentum. The de Broglie's theory is a little later thing.)
    First, using only the Maxwell's theory(not using the idea such as the (de Broglie's) waves), the two slit behavior of the electron can not be explained.

    Its main problems are Helium(He) model by the Bohr theory and the anomalous Zeeman effect in 1920's (See this thread.)

    At that time the three-body problem (like Helium) was very difficult.
    "We should not be surprised that we have thus far not arrived at this goal, since even the astronomers have not yet satisfactorily solved the three-body problem in spite of efforts over centuries' "(Sommerfeld 1919)

    The ground state energy of the Helium(4) which is known to be a correct exmerimental value now is -79.0054 eV.
    And the most latest variational method of the Schrodinger equation of He which is known is about -79.015 eV.
    This calculation uses many terms of the Hylleraas functions and is very difficult and complicated.
    But it is not -79.0054eV(experimental value).
    Because this value doesn't contain the nuclear movement(+0.011eV) and the relativistic effect(-0.0020~-0.0028eV) (by the higher electron velocity than the hydrogen).

    Here, these phenomina of the nuclear movement(this is the same as the electron movement) and the relativistic effects are related to the actual movement of the electron? Or not?)

    If we try to consider the electron as a real thing based on the Schroedinger equation(first, the probability density near the point at infinity of the hydrogen ground state is not zero), its motion would be probably complicated (not simple circular movement) and sometimes very fast. So to solve this, the charge of the electron must be discarded.)
    (Sorry. the BM persons. But honestly I think so.)

    Or the more superior theory is the MWI, I think.

    But for example, how do we explain the strange phenomina of the spin? (about the inversion by the 2 pi rotaion)? And the other problems in the Bohr thread which I said above?
  7. Jan 24, 2010 #6


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    Re: Bhor's rule breaking "energy levels"

    Well, this paper (http://arxiv.org/abs/0903.2546v1) claims to exactly obtain the experimental value using Bohr-model method. I have not had time to go through it in detail, but the conclusions seem highly counterintuitive at best.

    Dirac discovered that the concept of spin emerged naturally when deriving a relativistically consistent form of the Schrodinger equation. His insights provided a theoretical justification for Pauli's empirical description of the two-valued nature of electronic, and more generally fermionic, wavefunctions. The wikipedia entry on the Dirac equation gives a nice description of this, with some short derivations and mathematical illustrations
  8. Jan 24, 2010 #7


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    Re: Bhor's rule breaking "energy levels"

    I don't think this is true now, nor was it true when Bohr presented his model. I am an experimentalist and it is not at all unusual for me to use models which do not "make sense" when I design and interpret experiments. I don't mind making "strange" assumptions if it leads to models that fit my data, the mere fact that the models DO fit means that they tell us something about nature work meaning they are correct. Explaining WHY we can make these assumptions work is something one can worry about when designing the next experiment.

    Ongoing research is a process, it is only in hindsight that it becomes clear how things fit together.
  9. Jan 24, 2010 #8
    Re: Bhor's rule breaking "energy levels"

    I like it when things make sense. I don't think it's a good idea to tell yourself it "doesn't matter" whether or not something makes sense as long as it "works". I'm sure people do it but it can't be a good thing. People should try to make sense out of what they are doing.
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