Re: Binary stars

[Jack Uretsky <jlu@HEP.ANL.GOV>]

        There are good models and there are bad models.  Note that
Feynman, in his lectures (I-38-6) is quite careful in his discussion
of what we might think of as the Bohr model.
        Your model violates fundamental principles, and what I think is
worth discussing is what is violated by the model.  That's because your
conclusion depends upon the violations.
        The crucial point is the uncertainty principle.  Your picture
violates it in the radial direction (a radially confined orbit can only
be approximated with very high l so that there is a substantial angular
momentum barrier), and in the azimuthal direction perpendicular to the
orbit.
        The Bohr model itself was a device for calculating energy levels.
Nothing else about the model, that I can think of offhand, worked.
        When dealing with models, it is crucial to understand their
limitations.
        I trust that I've said enough on this topic.
                        Regards,
                                Jack


Adam was by constitution and proclivity a scientist; I was the same, and
we loved to call ourselves by that great name...Our first memorable
scientific discovery was the law that water and like fluids run downhill,
not up.
                          Mark Twain, <Extract from Eve's Autobiography>

On Sat, 18 Dec 1999, Ludwik Kowalski wrote:

> As I recall  there were no dipoles in the semi-classical
> (Bohr, 1913) model of orbiting. All orbits are circular,
> but only those orbits for which the angular momentum
> is an integer of h_bar are allowed. Wasn't the model
> with several L, for a given n, introduced later?
>
> What rule did I violate by allowing circular motion of
> two particles, and by calculating the necessary speeds?
> What would you do, Jack, to calculate v semi-classically
> from L=0?
>
> I guess you would say it is not possible. Yet many
> predictions of semi-classical models are in good
> agreement with experimental facts. Look at Rutherford
> scattering, for example, or Balmer's series. Sure it does
> not explain everything. But we know, more or less,
> when not to use it (when lambda becomes comparable
> or larger than "sizes of our systems".
>
> Yes, this model is very primitive by today's standards,
> but it is better than nothing. Would you agree that it is
> not a bad idea to try a semi-classical model first and
> then to decide what to do next?
>
> Many of us never advanced above the simple Bohr's
> theory. What is wrong in trying to use the tools we
> have? Teaching an introductory physics course is not
> the same thing as contributing to progress of science.
> It is an exercise of thinking about word phenomena
> in terms of models, old and new.
>
> Jack Uretsky wrote:
>
> > l=1 is a dipole.  But I mis-spoke, of course; l= 0
> > is spherical, not circular.  I stand by the rest.